Death isn’t an automatic rating bump, mild/cartoon violence is fine. Although you’d probably want to minimize how often it’s implied that someone dies from a ship exploding, having a bunch of side characters die in battle is likely going to bump up the rating. It’s also more acceptable to let bad guys die than good guys, that’s why thousands of goombas are stomped and it’s okay. Especially if they aren’t human (aka monster, robot, alien, zombie, etc). But Bowser never actually dies, he always comes back.