Would you play a very violent Mario game?
If it had actually violent animations, then yeah. If king koopa didn't had such a cartoony design and looked more like a dragon, and actually breathed fire. Right now it feels more like a joke.
Watch/play this instead, this is much better.
https://www.youtube.com/watch?v=JWfzVN_LHbw
[Vinesauce] Vinny - Terminal 7: A SourceMod Game
https://www.youtube.com/watch?v=ejNqrU94QtQ
[Vinesauce] Joel - Mario 3 Russian Genesis Bootleg
I'm pretty sure it isn't actual bootlegs but just shitty homebrew. No way shit like that was actually sold in real shops, but spreading shit like that online is quite believable.
I'm trying to think of actual good violent games, but can't think of anything but demonophobia. I guess Condemned: Criminal Origins counts, though in that you kill out of fear rather than out of desire to kill, it doesn't feel violent enough for me. The golden standard of violence for me are fighting scenes in Agharta manga, fights in that are so delightfully brutal that no videogame will ever come close.