A little robot on wheels that, once Mario gets close enough, stops moving and starts a fuse.
When the time is up, it explodes, but before doing so, it'll eject a small copy of itself out of its helmet, that grows to full size once it lands and repeats the cycle (until Mario cruelly stomps it).
Fuse timers are adjustable, meaning it can get quite dangerous and much harder for the player to stomp if you set its fuse lower, while longer fuses make it a lot easier to navigate around.
Graphics are included, they use up the unused tiles in the Spiny/Wiggler GFX file, but there are defines to easily move its graphics (and palettes) around.
Sonikku has shown a trick with his big Milde where you can store the sprite level index to its new sprites so the original sprite doesn't respawn until all its smaller Mildes have been despawned or killed.
The reason why it's important is because once the original robot explodes, the original Robo-Eject is now marked as "killed" even when it shouldn't from the gameplay perspective. The trick (which he speculated, give credits to him for that idea) is used so the new Robo-Eject counts as if it has been placed in the level.
Also added a JSON for custom sprite display and added enemy tag.