In Thaumcraft 4 and 5 there was a system where mobs have a chance to spawn as a champion variant similar to mods like Champions and Infernal Mobs but does it in a more interesting way in my opinion. In Thaumcraft 6 it seems to be mostly missing and mobs never end up spawning as a champion variant except for the bosses which cannot spawn in normal gameplay unless you're playing with Thaumic Augmentation which does use some bosses for the spire dungeons.

Maybe this can be added in through a config where you can control which mobs can spawn as a champion, what attributes to blacklist it as (i.e. let's say I don't want zombies spawning with the infested attribute), the chance of spawning as a champion and what drops they can have to replace the treasure bag drops. I'm not sure how difficult it would be to implement that but the champion mob system itself seems to be fully functional in Thaumcraft for the most part. If that isn't really something that belongs here though I understand, I thought it would be interesting to suggest it! ^^;