Undertale - Dusty Dino

It would have been a lot less anticlimactic if instead of Mettaton NEO getting destroyed instantly, you kill Alphys or she jumps infront of Mettaton like with Undyne and then upon seeing this, Mettaton transforms into his NEO form and sort of like Undyne's undying mode he also becomes a formidable opponent rather than being one-hit killed.