Last Resort inflicts damage and has no secondary effect. Last Resort will fail unless the Pokémon has used all of its other moves at least once while on the field. Using a move before switching out and back in does not count towards being able to use Last Resort. Last Resort will fail if it is the only move the user knows, or if the user does not know Last Resort (such as if it is called indirectly).
This move can be used only after the user has used all the other moves it knows in the battle.