As has been previously mentioned, Rhine didn't spend a lot of time accompanying Batman on his usual beat. This became even rarer after they figured out the soul-fragmenting trick, sending a weak copy of themselves to hang in Batman's shadow, able to build their reputation and contribute minor magical assistance without actually doing anything important.
However, 'rare' was not 'never'. Every night, Tanya performed a divination on whether or not Bruce was going to face challenges, enough that he truly fears for his life, that night. Most of the time, the magical augmentations that Tanya incorporated into the Batsuit (Tanya absolutely did not tell him that the golden liquid that she mixed into a polymer for integration was Rhine's demonic ichor, extracted from that damned biomechanical heart) was plenty to make the answer to that question 'no'. If the answer is yes, she performs a second divination to make sure it's not just him getting dosed with fear toxin again, and once that factor is accounted for she only pretends to send a fragment of herself and instead leaves one behind to do what most people do in the middle of the night: sleep.
It doesn't actually help her rest to do this, but Bruce is intensely uncomfortable with the idea of prophecy (which Tanya could understand, it took her a while to wrap her head around it as well) and thus would attempt to avert said prediction on principle if he knew the results (within reason). Thus, the deception.
Still, with Batman being supported by the real Rhine after the tremors of some grand danger echoed backwards through time loudly enough for them to detect, the night started off rather simply.
Batman's night, absent of any active disasters, begins by him going over his unsolved cases, plotting out the locations he'd need to go to gather more evidence, adding to the list of things he should be watching for to potentially open the newly cold cases back up, check his backdoor into Arkham's monitoring systems (not just built by Waynetech, but also donated for free. Bruce had to be reminded that 'so the patients don't break out as often' was a perfectly understandable reason that he didn't need to find a cover for) to check which patients were accounted for (that wasn't to say that it was a 100% reliable source of information, but it was a good start), determining which regular haunts or recent suspicious property acquisitions needed to be checked for anyone unaccounted for, and then having his fancy alien tech supercomputer calculate the resulting traveling salesman problem once his list of destinations for his night of detective work was determined.
He then proceeds to actually sojourn out (the next semester of school had already started, so Jason was back at home) when the sun finally sets completely, because all of the above occurs before that point. The Bat Signal is usually lit at this point, adding 'visit Gordon for strategizing' to his itinerary, but he always adds the GCPD building to his list of destinations anyway, just in case.
Most of the cases that Batman pursues were just whatever the GCPD threw away for lack of evidence, or were handled by identified corrupt elements, or sent to him by Barbie for further review. On the way to such places, any fresh crimes that pop up from his (well, Barbie took them over and keeps them up to date now…) taps into the GCPD's systems or any of his other numerous local-level sources of information get addressed immediately if he's close enough to respond, depending on urgency.
As this was Gotham, the ratio of random crimes stopped to planned investigations was somewhere around 1.7 to 1, and numbers that low required higher standards for what constituted a crime to stop instead of the vigilante equivalent of taking a moment to admire and possibly swing around a particularly weapon-like stick, a common pastime for children everywhere, in every dimension.
It was about two hours in, while Batman was driving the Batmobile, that he spoke up: "You're really here." He said idly. It was not a guess."
Rhine manifested out of Batman's shadow into the passenger seat, quickly putting on their seatbelt; it was a little awkward to wear normal ones with their wings, but the Batmobile's seats had a three point harness with a little extra room in the right spot that accommodated them easily. "On reflect? Correct." They said. Was it weird if they were oddly touched that he could tell? Their fragmented selves had very little personality: they barely spoke, performed limited magic impulsively, and manifested basically just to scare people. At least, the fragments they sent with Bruce did that: it was hard to sleep when more than ten percent of their mind was active elsewhere. There were a few recordings Batman could play to further the illusion that they were truly there, and he even played one earlier. Their reaction to that was probably subtly different enough that he was able to pick up on the fact that they were merely pretending to be a barely sentient and absolutely non-sapient echo of themselves.
"Is there something happening tonight?" He asked.
Instead of answering, Rhine withdrew a long narrow knife, crafted of an alloy of ectoranium and nth metal, lined with silver runes. It was made for thrusting, instead of cutting. "Instead of resting, I'll be testing." They said.
"...a Misericorde." Batman identified immediately, noticing the style and probably also picking out at least the rune that meant 'mercy'. "What is that for?"
"The blade of mercy kills, wrought to sever butcher's bills." Rhine said vaguely. It was the result of Professor Blood's research, supposedly it should be able to be used to sever the bonds between the Joker and his enslaved souls. "Made to spare the souls in town," Batman scowled the instant the subtle emphasis they used on the rhyming word was spoken. He knows exactly how this sentence ends. "used against the killer clown."
"...You're the reason Professor Blood has been acting like a lottery winner." Batman deduced. "He's been making many reckless purchases recently." Rhine's seen the car. Sure, Bruce has dozens just as nice or nicer, but the occultist was quite proud of it.
"He was paid for services rendered, he performed his task so payment was tendered." Rhine said, offended at the accusatory tone. "This weapon may still fail, full payment at the end of the tale."
"You're not killing The Joker." Batman commanded.
"That would be a separate action, it is fine to put him in traction." Rhine said, waving off his demand. "This knife's design is quite benign. He enslaves the dead, I'll free them instead."
Batman gave an approving grunt.
-----------------------
The event that Rhine's divinations likely detected occurred around one in the morning, five hours into the patrol. It started simply, with the Riddler using a drone to project his face onto a building's facade. "Riddle me this, Batman, armor-clad man." He began, as he was wont to do. Wait. Why did he add a rhyme? Rhine didn't like the sound of that, and not just because the rhyme was terrible. "Who is trapped within my lair? Whom shall die in dramatic flair? They blow, they pluck, they bow and hit, but led by one who does none of it."
Edward Nygma, a genius born to anti-intellectuals of parents, abused at home and at school, was a rather pathetic figure, when you got right down to it. While his origins were tragic, to be sure, his choices as a result of that origin were detestable.
However, he fell into two categories which meant that Batman used the kid gloves when dealing with him: First, he was genuinely mentally sick, not just an egomaniac. Any time he wasn't trying to prove how smart he was tended to be spent in a depressive spiral of self-hatred, convenient for keeping him out of trouble but also deeply disturbing to witness. Second, he was one of those supervillains that are less concerned about doing crime than they are antagonizing Batman, and that meant they were occasionally useful. Nygma specifically was easily manipulated and sometimes even pleasant when he was on his psychiatric medications, if they ever needed an extra brain to throw at a difficult problem. Needless to say, this didn't happen often.
Rhine didn't approve of how lenient Batman was with the repeat offenders, but it was an old argument so they didn't say anything.
Batman didn't lose a beat, accessing his speakers. "Where did you take the Chicago Symphony Orchestra?" He growled. They were in town, after all… This was why so many touring entertainers didn't visit Gotham… Odds were low that they'd still be performing tomorrow even if they survive this… there goes tomorrow evening…
Still, what kind of fresh hell did Edward cook up this time, to trip her divinations? "Nothing yet, Dark Knight!" The Riddler said, "You'll want to be right." He said, finishing the rhyme. Is he making fun of their speech impediment? "As for where you can save their lives, seek the place where madness thrives!" Well that narrows it down…
Still, indulging the Riddler was more Batman's thing, so as Nygma continued to spout oddly rhyming riddles to narrow his location down for Batman, they took out their tracker. Unfortunately, unlike some of the other supervillains, Rhine hadn't had the chance to steal a bloodied something or other for Nygma, so instead they closed their eyes and concentrated, focusing on the man whose image they had just seen. Normally, this wouldn't work, even with all their practice using tracking spells, but as the man was talking to Batman and Rhine intentionally, that created a tenuous connection that they could grasp. It even worked on recordings, although the length of the delay increased the difficulty.
Even if it wasn't live, it was still made recently enough. After a moment… "Our prey is that way." Rhine said, pointing forward and a little to the left.
"I know." Batman said, "Were you paying attention to the riddle?"
"You know the answer's no." Rhine said petulantly. "Nygma wishes for a pawn, but I will only yawn." Batman preferred to, when dealing with hostage-takers of honor like Nygma, play along and engage them on their preferred battlefields. He was soft-hearted like that.
"Just stay in my shadow; once we know how the hostages are secured, then you can intervene if you think you can." Batman instructed.
Understood…
-----------------------
When Batman managed to make it to the abandoned scuba diving school that had line of sight to Arkham, Rhine ducked into his shadow, but the instant he launched himself through a wall to make a dramatic entrance, something… strange happened.
"You're a thug and a fool, who's fallen into my trap!" The Riddler crowed, "A broken wall's a broken rule, penalty's a snap!" He snapped his fingers, and there was a twisting of space, resembling a form of magic that Rhine didn't use much: contract magic. "For breaking the walls, there will be extra balls! Avoid them all, unless you'd like them to fall!"
The screen that held Nygma changed to showing members of the orchestra dangling over what appeared to be an empty swimming pool of exceptional depth with a magic circle on the bottom. At a glance… Those were Egyptian hieroglyphs, so that was a bad sign. Rule of thumb: rich ancient cultures had the really big ticket ritual spells. They'd need more time to puzzle out what it actually did.
Still, that empty pool had a depth of twenty meters, so that fall was incredibly lethal. It did seem oddly easy to rescue, so Rhine was suspicious. As Nygma continued to outline the rules to the game slash obstacle course that Batman would have to traverse to rescue his hostages, Rhine felt out the Order magic that the Riddler had laid around the area.
By the time Batman commenced the game, Rhine felt that they had a good handle on it: In return for voluntarily shutting out his ability to cheat his game, he can create rules that, if broken, generate magic for him to wield in punishment depending on the severity of the transgression. It was complicated to set up, requiring a fair bit of power to kick start, but it felt like Nygma drew on the cruelty and sadism of Gotham's mana field, literally using how unfair and demented his game was to power his ability to force Batman to play by the rules of said game.
Okay, since when was Nygma this good at magic? Bullshit! The man in question was, fortunately, bragging about just that right now. "Magic isn't nearly that complex, Batman, even if for most it would perplex. With a mind like mine, simplicity is a spell's design. No more will you cheat my games, I will win and achieve my aims. Even your demon will dance to my tune, my superior rhymes will prove it soon."
Batman sighed. "Riddler." He deadpanned, "If your goal with your rhyming is to insult Rhine, you're wasting your time. She's not going to even notice."
"Her rhymes are bad! They make the listener sad!" The Riddler retorted, still sticking with his schtick. "I will prove my dominance, rise up in prominence!"
"Rhine hasn't paid attention to anything you've said in years." Batman said bluntly, "If she had her way, you'd be missing your tongue already. She hates riddles."
Nygma sputtered at the words. "What do you mean she- I'm going to- that's it it's time-" He paused. "Oh. You're trying to trick me." He concluded, "Ensure that my traps pick me. You see that I've created a spellcraft trap, daring you to turn this into a scrap."
Batman paused. "Rhine. Report."
Rhine let their face emerge from Batman's shadow, right in front of him. Looking up at the vigilante, they spoke: "Contract magic, perverted, it's tragic." They said, "Historically used by courts of law, a two-edged blade is its primary flaw."
"Is his rhyming part of it?" Batman asked.
"It is, in fact. He spoke without tact, so the spell react." Rhine gathered the energy created from his mild transgression. "Enough to save one hostage, brave." They cast the power, laced with intent, along the structures the contract magic prepared. On cue, one of the hostages on the screen vanished, whisked away by the spell to a safe place. Due to their enhanced magical senses for being in demon form, they saw that the violinist landed in their hotel room. Unlike simply doing this with their own magic, by doing it as their 'prize' for the game, it wasn't cheating.
"How was he able to ensnare me without my permission?" Batman asked as he turned to the next section of the obstacle course, plotting his route.
"Your arrival had intent to play his game, unwillingness to play you cannot claim." Rhine explained. "I was to let you play and assist, so my agreement here I cannot twist. Furthermore, my nature's a bore, I cannot lose his rhyming test, so I cannot refuse to let him contest." In other words: you could absolutely force someone into a contest where they absolutely cannot lose, where all you're doing is putting restrictions on yourself. This is rarely useful, but is potentially exploitable: if they were to turn human, they'd still be part of the rhyming contest, and thus energy would be built up by Nygma for their transgressions. "It's really quite complicated, the Lords of Order are intoxicated." Because they're the ones ensuring this framework exists. The question was: did Nygma have an actual plan with that, or did he just misunderstand something? There might be something they were missing…
"Hm. Noted." Batman said, gesturing for Rhine to go back into his shadow.
"Yes, Batman, you're trapped in my web!" The Riddler crooned, "Tests and danger, your life will soon ebb!"
Soon enough, after even more rhyming taunts and riddles, Batman finished the obstacle course. "You may have completed my basic test, but will you be able to complete the rest?" The Riddler shouted, which freed up a rather large amount of magical energy for Rhine to direct. Several more of the hostages were teleported away. Sure, they could wait for the whole game to be over and let Batman just demand the hostage's release, but this way some of them got to live if they all died.
As if summoned by that morbid thought, a gunshot rang out, and two of the hostages suddenly fell to their deaths. The transgressive energy surged, although it was different than before: this was power reserved for punishing rulebreakers, not for claiming prizes.
"AHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!" The Joker laughed, gun in hand. Rhine immediately went through the walls to the hostage area, expending the order magic to allow them to do this without transgressing. The magic circles that now had the corpses of two of the orchestra members started to glow, but the Joker jerked his offhand and the power, as well as the ghosts of the orchestra members, started flowing into him.
"The Joker. Mediocre." Nygma said between clenched teeth.
"Eddie!" The Joker said, scowling. "I am not happy. Here I was, about to unleash my most hell-raising plot yet, and also secure some sweet background music, when I find out that YOU STOLE MY IDEA!" The Joker leapt at Nygma, but was interrupted by Rhine stabbing him in the chest, directing the order magic to ensure that he doesn't steal the prize and is further punished with the loss of more of what he tried to steal.
With the focus created with Dr. Blood's research, already intent to do just that, the Order magic leapt to their assistance: the orchestra members were sent off to their final destination, and the Joker screamed as dozens more of his ghosts also shuffled off to the afterlives appropriate to them.
They could use their own demonic magic and thin but extant claim over those souls to ensnare them, either to eat the souls or for some other purpose, but Rhine instead immediately relinquished any such claim and let them go where they will.
Still, the Joker has additional tricks, so with an exertion of brute strength that broke all of his bones before he passed that damage on to his ghosts, Rhine and the misericorde was thrown off of the clown, slamming into a wall with… well, it was less force than was needed to even bruise their demonic flesh.
"What did you do?" The Joker asked dangerously.
"You interfered with my plot." The Riddle explained, "Your actions thus go to naught."
Idly, Rhine noticed that on the wall of monitors that Nygma had set up, Batman was going through the next phase of the twisted game while the villain was distracted.
"Not that!" The Joker spat, "You stole something from me." He said accusingly, pointing at Rhine with his pistol. "How?"
Rhine giggled. "You ask a demon how they steal souls? You might as well ask about your hand's controls. It's like suckling a teat, souls are what I eat."
"Those souls were mine!" Joker insists, which, now that Rhine thought about it, was the first time he actually acknowledged they were there. So he did know what he was doing. Richard was convinced that he was doing all that stuff unconsciously. "Give them back!"
"I would if I could," Rhine lied, "but even if you opened your gob, I cannot poop, so you'll have to sob." They giggled at their own joke.
Nygma's face twisted in disgust at Tanya's toilet humor. "God no." He muttered, which made him lose more points in the rhyme contest. Idly, Rhine directed it to claim… it was enough for three more orchestra members, plus twelve more from Batman's continued progress. About thirty left.
Joker laughed at the joke despite himself. "So the demon has jokes, eh?" He said, being one of the local villains with the least experience with Rhine. The most experience with getting stabbed by Rhine, though… "What would Bats have to say if he knew you were cheating on your diet, hm?"
"I'd simply deny, for I rarely lie," Rhine taunted, smug like a liar. "-that he would buy, so go and try." It also helped that Batman would know that they only pretended to eat the souls. …right?
The Joker laughed uproariously, finding their response hilarious. "Oh, I love you, kid!" He said, the word being unsettlingly on the mark. What did he know? "I knew you had Bats wrapped around your pinky finger, acting all nice when you're a killer at heart."
"Nevertheless, you are interfering with my plot. That is something to tolerate? Not." The Riddler said authoritatively, constructing a new facet of his contract magic ritual. "You want to kill the Bat, ruin things? You'll be playing with my strings."
It was a little interesting, seeing Nygma so expertly manipulate the Order aspected magic to draw in the capricious cruelty of Gotham and make use of it to enforce horrendously unfair conditions within the arena he had prepared. It made Rhine wonder what he could do if he were to bend those talents to something a bit more constructive?
"The Bat's that way, to save the day." Nygma said, pointing to a door. On cue, it opened. "Go and fight him, one on one. I had a robot I was going to run, but I'll save it for later, as the creator. It'll be the fairest fight in this night: Skills, strengths and magic boost, averaged out, contest produced." He looked at Rhine. "No interference, rules adherenced." He added.
"The Bat's arrived, go to your suicide." Rhine added.
"Fair fights are for suckers." The Joker said, "Good thing this isn't one: I have one thing he doesn't, after all!" He chuckled. "Or rather, he has a weight around him that I don't!" his chuckles exploded into full laughter as he ran through the door.
"As for you and I," Nygma said, "-another contest, rhymes don't fly."
"If you'll say I win for sure, I'm willing to change it premature." Rhine added, "Without a shift, nothing stops me from making a rift." They gestured with the knife, to emphasize their threat. This was a bluff; while yes, the rhyming contest created an implicit ban on violence, the implicitness of the rule weakened the transgression, and if they killed him, it wouldn't matter how many rules they broke to do so, he couldn't enforce them.
The Riddler swallowed thickly, realizing his mistake. Surrender the rhyming game, removing his leverage? Or risk that the demon who just admitted to eating souls without Batman's approval would stab him with a knife? Even if he was willing to trust in Batman's rule, how well did he know the efficacy and weaknesses of his chosen specialty? Demons were vulnerable to this kind of thing, but much like holy water, the purity mattered.
Your move, Nygma…