Missing animations
Some monsters are still missing their animations. I have encountered a few of these already, and decided to maintain a list from now on so next time I see one, I can add it here. I'm fairly sure these are known, and may in fact already be implemented in 3.0.0 (sadly I don't have prerelease access), but just in case any one of these has been overlooked:
Vortices
Yggaz, the fool
Shopkeepers
Fairy dragon
Mimic/Greater mimic/Mimic hivemind
Dorn Beast
Balor
Giant eel
Shyssiryxius
Ancient dragons
(Vortices in particular are deserving of some spectacular animation, I think -- which may also be the reason they're not in the game yet. :) )