Things You'll Need
Instructions
Fight the Emperor Ing until it's in its final phase (Mutated Emperor Ing) and position yourself directly in front of (or even underneath) its body.
Use the Screw Attack and roll as close to the bottom of its body as you can, being careful not to crash into any of its legs; your target is an invisible area behind its upper legs. Attempt this just as the boss is beginning to jump (as you can Screw Attack underneath it) or immediately after its heart changes color (as it will be motionless for a brief moment) for the best chance of hitting this spot.
Check the Mutated Emperor Ing's health bar to see if you did it successfully (there's no other way to know, as the boss will show no visible sign of damage when you hit it); if successful, very large portions of its health will be gone. Screw Attack the boss repeatedly until it is dead.