The Altering Cave (Japanese: へんげのどうくつ Changing Cave) is found in Pokémon Emerald, FireRed and LeafGreen.
At first only Zubat can be found in this cave, but by using Mystery Gift with other players, other Pokémon such as Houndour and Stantler can be unlocked.
In Pokémon FireRed and Pokémon LeafGreen, Altering Cave is found north of Fortune Island on Outcast Island.
In Pokémon Emerald, Altering Cave is found on Route 103, on the east bank of the pond that passes through the center of the route.
Mirage Caves • Mirage Forests • Mirage Islands • Mirage MountainsCrescent Isle • Fabled Cave • Gnarled Den • Nameless Cavern • Pathless Plain • Trackless Forest