Fear and/or KD make the most sense to me for control effects for Beasts, since being attacked by wolves and lions is scary and they're big enough to tackle a person. Slow could work, too, as the aftermath of a leg injury, and maybe Stun like if they surprised-pounced on you and smacked you in the head or something. Not sure about debuffs, but -tohit seems to go with Fear most of the time. -Def would work for similar reasons to Slow; after being injured, you can't dodge as well. Also, possibly, because most enemies aren't used to fighting animals so they're not sure how to anticipate their attacks, making them harder to dodge.
Just my 2 inf.