The game is fantastic. If you wanted to do a boss fight with Puro, that's cool. One recommendation I would make to the existing version as is, is the Pacifist run should have a quick cutscene with Squid Dog.
Maybe have the giant make a hand heart gesture? To let the player know he approves of their no-violence run, rather than it briefly "glitching out" to the next area. When it first happened, I thought the game was bugged and accidentally skipped a boss fight.