unkilable monster

I have mmeet a monster in vall factory that I cant hit and of course it wasnt proximal tangbility (even didynt see his life bar ) and another problem i have meet is on one map with boos I couldynt leave a boos arena so i couldynt finisht a map :( that map with unkillable monter also unfinishable. I have got a video but cant post it here.