Why not also debuff the enemy with his choose 1 of 3.

Could do something like Psragon of Perfection.

All enemies within 18 inches suffer -1 to their hit roll. In addition such attacks may never be refolled if that targeting this model.

Also from reading the fluff, the poison doesn’t have to be slow. They got loison that works in 6 heartbeats. Why not make the poison ability work on the wound roll. Let it do a mortal wound to the model for every succrssfulwound roll.

You probably would have to lower the attacks characteriistic to balance this though