I am here to add to the avalanche.
Alright let see what i can think off. Hope i am not to late :p. Tauros crest: Return the to gen 1 crits tied to speed. The faster tauros is the more likely that he will crit.
Brings back our good old bull and makes him usefull.... sometimes. Miltank crest: Lactose intolerant. everyone dies of diarrhea. That's all.
In all seriousness maybe that's not such a bad idea. All healing you get or food you consume when she's out will give you an ailment for a few turns ( overtime damage or poison damage). Makes milkyway extra annoying. Nidoqueen crest
