megas by definition wins by 'finds a way.' if you've got a way to be beaten, it somehow knows exactly the way to do it, even if it's through a bizarre process involving knowledge it shouldn't have and exact timing. it's effectively an oversized reality warping mech to fit the situation and get a win.
and it ain't like she's got full immunities to everything or something - early on you're told about how Negi's dad gimped her with that anti-vampire soup or whatever he had her fall into that made her go from hot 20 year old to a gimped loli. and then she got sealed on top of that.
--
The future must protect the clone's past.
"Maybe it's a tentacle, molesting the planet itself. - Aschen Brodel.