I remember the blitzcrank mobile game. It was one of the best mobile games ever made.
We're looking into this closely at the moment (we've seen it too under certain conditions). We suspect it has something to do with the "Soul Fighter" tab to the left of the Tournament of Souls tab. Please try disabling the "Motion" toggle on that page and let me know if it's still absorbing a huge amount of RAM or CPU resources.
The mini-game should not usually take up more than 1-1.5GB normally.