RE: The Competitive Battling Simple Questions Thread
From Smogon:
Whenever a Pokemon holding a Life Orb successfully uses a damaging attack, that attack deals 1.3x its normal damage, rounded down, and the attacker loses 1/10 of their maximum HP, even if the opponent is behind a Substitute. Damage rounds down to the minimum possible value for 10%—thus, if the Pokemon has a HP stat ending in any number indivisible by 10, it can use Life Orb 11 times without dying. If a Pokemon has a HP stat of 19, then Life Orb will deal 1 HP recoil per attack, so the holder can attack 19 times at most. If the attack fails, adjusts HP instead of dealing damage, or if the holder's ability is Magic Guard, or if the holder's ability is Sheer Force and the attack was boosted by Sheer Force, then the holder takes no damage from Life Orb. For multi-hit attacks, all hits are treated as a single attack for the purposes of Life Orb recoil. If the Life Orb holder uses Circle Throw or Dragon Tail and then faints from the recoil, the target is not forced out. If a Pokemon steals Life Orb by using Thief or Covet, then that Pokemon takes recoil damage afterwards.
For Lucario, it is often the item of choice. Most Swords Dancing Lucario will have it. It's imo the best overall item for set-up sweepers and all-out attackers, as it gives a great damage boost whilst allowing the freedom of changing moves.
~AoH