Did we mention the doors lock so you can't leave the room? Play on Hard and/or a 15% run, and you'll soon find yourself out of Missiles, desperately re-freezing every Metroid surrounding you and picking off every Rinka in hopes that it drops a missile this time. Add this to hazards like lava in some of the rooms, Rinkas that are a nuisance, and thus it only takes one trip from a missed obstacle to fall and become Metroid food. They come in groups, so you might freeze one Metroid only to find yourself backed in a corner with another waiting on the other side of its frozen friend, ready to grab you as soon as you kill it. If one latches onto you, you can deploy a bomb to make it let go, but drop too many and you'll accidentally bomb jump back into its mouth. Freezing them wears off faster than most enemies, and it's only when they're frozen that they can be damaged, and then only with missiles.