I think it looks neat.
It’s 4x weak to fairy, for one.
Is that the only thing?
It is intriguing, but in reality, between the dominant force of Fairy/Psychic offense and defense in on that is Delta Bulbasaur, and the unbelievable appeal of a skeletal undead Charizard, it really just falls out of the spotlight.
Is it usable?
Of course, his Mega is an utter tank. High defenses, Mega Launcher to make his two of his best moves, Aura Sphere and Dark Pulse, even better. The only thing really wrong with him is his low speed, and he’s completely helpless against Fairy-Types. Also, his shiny looks like Bowser
I used one in a randomized playthrough and it won me the game, so I like it as well
For me, it’s my least favorite because they went with the obvious route. “Oh. A dark fighting Squirtle? Make him a Ninja.” It’s too obvious. Especially since I’ve seen the ninja squirtle concept many times already.