Drains HP from the target and transfers it to the spell caster.Description
Drain is learned from the Oak Staff for 60 AP, which can be stolen from Ralvuimago and Soulcage, found in Chocograph 11, Small Beach, and bought in Conde Petie, Black Mage Village (discs 2 & 3), Alexandria, Treno (disc 3), and Ipsen's Castle Mogshop for 2,400 gil.
The earliest to get it is from doing the Chocobo Hot and Cold minigame to upgrade Choco to a reef chocobo at the first chance and then digging up more chocographs at the Chocobo's Forest until "Small Beach" treasure becomes available. The player could get the treasure before going to Burmecia.
Black Magic spells are based on Vivi's Level, Magic stats, and the Spell Power of the spell. Vivi can use the Focus ability to increase his Magic during that battle by 25% per use. The effect stacks up to 99 and lasts for the entire battle, even if KO'd.
Where Rnd means a random number, while MOD means modulus operation. "Rnd MOD x" can be read as a random number between 0 and x-1.
In Vivi's Trance, Blk Mag turns into Dbl Blk where Vivi can cast two spells on his turn. The spells cost MP and expend the Trance gauge independently.
Vivi can use Drain to replenish his HP on his turn. It is weaker than his other non-elemental spells, including Bio learned from the same weapon, but is slightly stronger than second tier elemental spells Fira, Blizzara, and Thundara, which in turn can be made stronger with equipment with elemental affinities, and enemy weaknesses to elements.
Drain should only be used when Vivi needs to replenish his health; the areas where Vivi is required to be in the party as part of the story (after the party has access to an Oak Staff to use Drain) where the party lacks a dedicated white mage are: Burmecia, Cleyra's Trunk, Cleyra, and Alexandria Castle. When there is a white mage in the party, Vivi is better off letting them heal and use his spells to target enemies' elemental weaknesses to maximum efficiency.
Drain can still come in handy situationally when only Vivi needs healing, it is his turn, and the enemy is not undead. A niche use would be to use it on an enemy who has Reflect and Vivi is not equipping Reflect-Null, as Drain pierces Reflect status naturally. However, only few enemies use Reflect: Ash, Drakan, Hades, Maliris, Ring Leader, and Trance Kuja.