A Move Deleter is the opposite of a Move Tutor. They will cause a Pokémon to forget a move it knows.

This is the only way for a Pokémon to lose HM moves, such as Flash or Cut. This is done so that a player will not get stuck in an area where an HM move is required to continue.

Locations

Move Deleters can be found in the following locations:

Blackthron City in Johto
Fucshia City in Kanto (FireRed/LeafGreen Only)
Mt. Battle in Orre