Terror of the Peaks auto target is self, meaning if you have too many terror stacks and run out of time arena auto selects yourself for any remaining stacks. Game example I had 81 terror of the peark stacks due to mirror march, and even with just mass clicking the opponent so each stack would apply to the opponent as soon as possible, arena timed out of 3 ropes and over 40+ stacks, then applied to myself.

perhaps a feature to select x targets for the same card effect going on the stack