No the Mountain has been poisoned. It won’t end well. Well, for him.
The scene in the coliseum was beautifully choreographed, but the Mountain knew, like we all do, you don’t stand too close to someone who is on the ground, even though you poked him with a poison spear, and you don’t keep monologuing and blowing kisses to your lady love, because that prone adversary, may have enough to take your head and squish it like a grape.