The thing is, the slime has a core. Losing the core ought to be a big deal. It might create a whole lot of clones, but I doubt it can clone the core. One would think the core noclipped through the ground into oblivion, inside the main body. So, that small thing would be a clone without the core. Unless Laspi stored the core away inside a small clone in the middle of the battle.
Huh, a time save via the glitch makes sense. The boss was still at 70% hp, then you glitch the boss out of the boss arena to kill. That's quicker than a sequence skip at 50% health.