>>33107911Megafug has some counters to it out of the 800 other pokemon. Gen 1 Mewtwo is among only 150 other pokemon, almost all of which are mediocre statwise. It has basically no weakness, because nobody's stupid enough to attack it with Pin Missile Jolteon, and it gets Gen 1 Amnesia.
At 780 BST, Megafug puts up with pokemon that have 680BST. Gen 1 Mewtwo has effectively 744BST due to its Sp Def being a full 64BST higher back then, and has to put up with what? Pokemon that have 500 or so BST, 600 at BEST with Dragonite and 610 with Articuno.
There's a reason it got a heavy as shit nerf.