Change your preferences here.
Deals damage. If the target has received damage on this turn before this move was used, this move's Base Power is doubled. However, if the target received damage by any of the following methods Base Power will not double: self-inflicted damage by using an attack (Curse, Belly Drum, or Substitute), hit itself in confusion, recoil from Struggle, or being hit with the move Pain Split. If the target is dealt zero damage from an attack that would have damaged it, except for the effect of a final modifier or the attack itself, then Base Power will be doubled.
Assurance is a rare sight competitively, as it faces competition as a physical Dark-type attack from the much more reliable Crunch, as well as from Payback. However, since Payback no longer hits with doubled power on the switch, Assurance is now the best Dark-type attack with which to hit a predicted Ghost- or Psychic-type switch-in provided that Stealth Rock or Spikes is present. Assurance also suits slower, more defensive Pokemon since its power cannot be doubled if the user moves first. Donphan is a Pokemon that may be seen to use Assurance, since it lacks a better Dark-type move, and has the above attributes, often needing to hit spinblockers on the switch.
Payback has the same Base Power, but its power is doubled instead if the opponent moves first.
Crunch is a similar move hitting with a reliable 80 Base Power, and with a chance to lower Defense.