The D&D system has been altered to make the story more entertaining, as some rules only work as a board game. The system of dice and luck to decide damage still exists, but some Feats and Spells had to be rewritten.
Something completely reimagined is the system of weapon and tool proficiency, which basically decides your skill with them and is chosen during character creation and rarely altered during all sessions. This works in tabletop RPGs, but in a story? I think not. I don't think tying the development of the character's weapon skill to a specific level from the beginning will make for an interesting story.
Since I don't want to stagnate the MC's power, I will change Weapon Proficiency to Weapon Talents, ranging from 0 to 4, with each point representing a 25% increase in talent compared to the average population. Jaime, for example, is a 3/4, while Arthur Dayne is a 4/4. Any talent that does not appear in the profile means it is automatically 0, which is the average.
Another thing is how HP works(This is for those already familiar with D&D rules. If you don't, just skip, makes no difference for you). The Constitution modifier is applied across all levels already passed. This means that even if you level up with a 0+ bonus, after reaching 1+ or 2+, it will be included in all past levels and automatically changed when it increases, just like in regular electronic RPGs. I made this decision because the D&D rule, in my opinion, only works as a tabletop RPG, where the created character starts as a fully developed adult, not a child as in this story, and then levels up, often with positive modifiers, not neutral or negative ones.
And talking about Classes. They appear on a person's profile a little late in life. Like 15 to 20, ater the person already made the decision about his future. The MC, because of the System, is the exception, getting his with 2. I am saying this because, as the first chapter will emphasize: the world and its magic have been altered by the arrival of the system. And the class that appears in the secondary characters' profiles doesn't just symbolize how they fight, even though the class grants less power than the MC would receive if they had chosen it. I won't give spoilers, but know that it will be important.
And the most important information, more important than me having altered some rules, is for those who do not know how D&D magic works. For the uninitiated, you can only use a limited amount of magic per day, and some must be prepared beforehand with a ritual. The only exception to this are cantrips, which are level 0, the weakest spells, and can be used without daily usage restrictions.
Another important detail is that D&D magic, even those with area effects, was not made to individually fight an army. Fights in tabletop RPGs are always between small groups, and the effects of the magic reflect this. So don't expect the MC to start casting magic repeatedly or be able to destroy an entire army. Quite the opposite. And it is this opposite that made me want to write this story. It's incredible how the D&D System aligns with the world of Westeros. Magic is powerful, but not unbeatable to the point of making the MC invincible. He will still have to use many strategies to overcome his challenges.
The last point I wanted to bring up beforehand is about power progression: It will be slow. Just like in the tabletop game and electronic games, it takes a long time to level up, and sometimes you gain almost nothing when leveling up. The initial spells are also not strong enough to make the MC capable of facing the whole world alone, as happens in other system stories; This is not a wish-fulfillment story.
But believe me (or look up the spells that Druids can learn yourself), the spells learned at the highest level are very strong for a Low Fantasy world like Westeros, to the point of trivializing certain problems. So, be patient.