Causes Non-elemental damage and Poison to single/multiple targets.Description
If Steiner and Vivi are in the same party (and neither is incapacitated in some manner), the former can also use Vivi's Bio spell in his sword magic, where the ability uses his stats rather than Vivi's, but it only boosts the power of his attack without the chance of ailment-infliction. In Trance, Vivi can use the spell twice in one turn.
Bio can also be used by multiple Demon class enemies, being Agares, Amdusias, Drakan, Ring Leader, Torama, and the Meltigemini. It can be reflected as normal and can be countered with the support ability Return Magic.
Bio is learned from the Oak Staff for 40 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, allowing access to Bio before Vivi can even learn Poison.
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.
Bio is the only Black Magic spell that deals both damage and has a chance to inflict an ailment onto the target(s). The ailment-infliction chance is a flat 20%, unaffected by the spell being multi-targeted; it will simply deal less damage this way.
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.
The damage formula for Swd Mag spells is as follows:
Bio is between Vivi's second and third tier spells; stronger than Fira, Blizzara, and Thundara, but weaker than Firaga, Blizzaga, and Thundaga; its MP-cost also reflects its placement. It is useful until the endgame for its flat 20% chance to poison the target(s), and is overall the superior spell to use over Poison, as the latter may be a waste of a turn if the ailment does not stick. However, Poison has a better chance to inflict the target. Vivi can boost damage with Bio with Focus, but the ailment-infliction chance remains unchanged.
For enemies weak to Fire, Ice or Thunder, the -ra tier elemental spells deal more damage and cost less MP, and are likely more desirable over using Bio even if the latter has a chance to also inflict Poison. Bio can be learned around the same time or slightly earlier as the second tier elemental spells if the player prioritizes doing the Hot and Cold minigame early.
As a Swd Mag, Steiner can use Bio to boost the power of his attack, but he does not poison his target. He is always better off targeting an enemy's elemental weakness, but if the enemy has no weakness to exploit, then Bio Sword is better than -ra tier spell swords.