Yaanei is finicky. He can be a kitten, or have a raging hard-on. The less TP he gets though the better. Once he gets down to 25%, if people feed him enough TP, he'll give you a hard time.
I've tanked it countless times as THF. Zombie and Terror/Bio is really the only dangerous part, and those won't directly kill you, only coupled with a strong hit will they be truly dangerous.
We fought this NM many times for Aias Bonnets to go around our LS. 9/10 it's a push over super easy fight... that 1/10 times it's like a serious wake up call and you're like wtf is going on here we actually have to pay attention? why is this dude so pissed he's going *** nuts on us. ahhhh just kill him already