How about the possibility of an upgrade to fading in/out during re-pops?
E.g.
Beetles crawling out of the ground, down from the trees
Monkeys dropping down from trees
Birds swooping down from the air
Ghosts fading in with style, like with an eerie black cloud...etc
No need to have anything too varied for now, perhaps one per mob family?
It will really set it apart from other run-of-the-mill MMOs around.