There is no true counter to the psychic phase
so you are boned there.
The chances of you dealing with the hoard of pink bubble gum is going to be tough. especially if they hide BLOS.
Best chance is to just gun them, get locked into combat and hope for the best on instability tests. or shoot the gak out of them with barrage weapons. and dont let them get the rerollable 2++ off the
ADL going to ground.
i feel best option is to
a) STRICTLY enforce the no model? no summoning thing. (no proxiying you dang cheapskate)
b) try to get as many objectives as you can unless you can some how manage to punk a unit or two of summoning horrors.
c) possibly have fun freaking them out with mr clux. or just mass damage them in
CC and hope for the best. (had a single ironclad go toss the salad of three full sized pink horror squad after dropping in. (they could NOT kill the dang thing with the bolt of change or whatever power they had (survived till T7 with 1
HP left



)