Final Gambit is an offensive Fighting-type move. The target receives damage equal to how much HP the user lost.
If Final Gambit fails due to missing, type immunity, or Protect, then Final Gambit fails and the user won't faint. The move's side effect is not considered as inflicting damage to the user, and so if the user is holding a Focus Band, Focus Sash, or has Sturdy, it will not activate and the user will still faint. However, the move inflicts damage to the target, and so the target's Focus Band, Focus Sash, Sturdy, and/or Endure can still trigger if applicable, so that the target will be left with 1 HP
Pokémon that learn Final Gambit
By leveling up
Via prior evolution