On the topic of Knights and Barons crossing acid, I do like the 'cost pathing' idea, maybe lower acid to 4. There are small differences in the AI of the enemies, as they tend to have different strategies. Humans run at you shooting dumbly. Sergeants wait out of sight for an ambush. Captains tend to just stand. Commandos roam. Imps chase you, but roam in a circle when they can't see you. Demons run around rooms to try and get to you, sometimes dieing from (legitimate) stupidity (seriously, I love that demons do this, it's fitting). Lost souls hunt you, little roaming, they sometimes pop through a door as soon as it is opened. Cacos roam, keeping at range, as do Mancubi and Revenants. Arachs hunt somewhat like Commandos. Viles keep out of combat, and even resort to distractions and hellspawn-shields. HKs and Barons should behave like kings, leading a charge perhaps, but not chasing mindlessly after the player.
Maybe they should take only 1 point of damage from acid.
Another thing that both HKs and Barons do is picking up EVERY piece of ammo on the ground. It's as if they are OCD. It annoys me, but makes it easy to know when one is around, with all the clacking of ammo being picked up. I don't know if this was intended or not. It is slightly funny seeing an HK explode like a pinata, dumping a ton of ammo when killed.
Oh, and I like cats. Especially wet cats. :P