ZDoom

You could override Tick() of the monster and inside, check for different player classes via CheckProximity or LineTrace or whatever, add them to an array if found and then use the array contents to determine which player class to target.

So, yes, it's possible if you know how to zScript.

Is it possible to set up character classes in a way that monsters will attack one class more often than the other?

For example: A barbarian and a hobbit walk into a room full of goblins. The goblins see the barbarian as a bigger threat, and will attack the barbarian more often. So when the barbarian and the hobbit encounter the goblins, each goblin has a 75% chance of targeting the barbarian, and only a 25% chance of targeting the hobbit.

Is this possible?