As of the new Sonic x Shadow Generations game, Mephiles is now pathetic as he drops his previous nihilistic personality and cowardly begs Shadow to let him live.
Technically he doesn't outright beg Shadow to let him live, he kinda has a breakdown where he says he wants to exist before sending his minions after Shadow, but yeah, I agree with you. Plus he's still pretty sadistic.
Maybe it is only a villainous breakdown and he’s reacting reasonably after his previous days removed from existence as Shadow seals him away. I mean, what else could he possibly say? A lot of villains are fearful of death but they react just as Mephiles only towards their defeats and they aren’t considered cowards. Not to mention, he still tried to attack him rather than merely kneeling down and begging for it.
I disagree with him being a Magnificent Baddie. I agree he’s too sadistic but I must point out that his big villainous breakdown at the end shows he’s really upset and that’s too wrathful for MB