Kago
Kagos are stationary enemies which have two parts to them: the small nest and the large tower.
The nest, unlike the tower, is invulnerable and is unable to damage Samus. It transforms into the 5-tile tall tower upon contact with an X-Parasite.
There are unused graphics and code for bugs. It is likely that they would have been spawned by the Kago nest when shot, similar to Super Metroid, but as there is no code associated for spawning them it’s not possible to know for certain. There is a
video
Additionally the Kago tower also has unused animations for
different speeds