Metroid Fusion - Unused Sprite Animations
There are quite a few unused sprite animations left in the game. There are also some unused enemies and invisible sprites that you don't normally get to see.
Some enemies have several unused animations. In particular, Halzyn and Serris have a lot of unused animations, implying some unused behavior.
I don't know much about the details of each unused animation, so feel free to speculate in the comments and I'll answer whatever I can.