More diverse behaviour would be nice. Though deer normally run away (really, they should run away even without being attacked), they could sometimes freeze. Also, elephants should not always run away, but should sometimes turn to fight. I'm not sure about level dependency, but not necessarily opposed to it either.

About implementation: creature behaviours are in ...server/creature/impl/, and it is probably not very difficult for even new contributors to create a new behaviour. And then the creature needs to declare which profiles it uses (in xml; data/conf/creatures/. There should be plenty of examples).