Poison damage + status change/one enemyDescription
Bio is an attack magic spell in Final Fantasy VIII. It is unique in that it is affiliated with both the Poison element and the status. This means it can be junctioned to deal or resist Poison-elemental damage, or to resist or inflict the Poison status on enemies.
Though Bio is the only spell affiliated with Poison-elemental damage, it is not the only spell affiliated with the Poison status, as Pain is affiliated with Poison among other status effects.
When Magic Booster is used in the 2013 PC re-release, the player's inventory gains 100 Bio spells, among other basic spells.
Bio can be drawn from a variety of enemies of all levels, but it is not terribly common. The Guardian Force Diablos' ability ST Mag-RF allows Bio to be refined from various items. The easiest way that doesn't require card games is to make them from Antidotes, a common item available from shops, as gil is usually abundant if the player has at all a decent SeeD rank. Otherwise, the player can procure Malboro cards to modify into their tentacles and then into Bio.
Bio has a spell power of 30 when cast, meaning its damage is calculated as:
It is cast as a spell in the Magic command, Selphie's Slot Limit Break, or Rinoa's Angel Wing if she has it in her inventory. It can inflict the target with the Poison status, which makes them take incremental non-elemental damage (thus it still damages targets that absorb Poison damage).
Bio is particularly useful for defending against Poison. When using Bio for damage, it is very effective against human enemies, but it is useless against Poison-based and mechanical enemies.
After Pain is acquired in sufficient quantities, Bio is rendered relatively redundant. This is because Pain can inflict or fully resist against three statuses, including Poison. While Bio can still be useful for junctioning to damage if the player has junctioned Pain to boost stats, it is often best to remove Bio in favor of Pain in order to have more spell slots available.