Onyx: They resemble the build of a rhino, they are hulking brutes that stand on four giant feet and trample over anything they can. Onyx are the least confrontational of the Entities when it comes to humans.
They perfer to hunt and target other entities that left a breach, and though rare there have been cases where they would rather hunt another Onyx than go after a human.
The cause for this is unknown as we can assume wherever the Breaches led from doesn't have humans because all other entities seem to have no problem engaging with humans.
Captain Corey head of Liquidation Team A98 once remarked "Their Buffalos! You want me to shoot Buffalos!"
And that sentiment is carried out by all Liquidation Teams in charge of Breaches where Onyx are active.