Casting Vanish on an enemy allows you to instantly kill them with death spells even if the enemy is immune to death.
The intended effect of Vanish was to have magic spells hit 100% of the time. The unintended effect is that it bypasses death immunity. All other status effects will still miss (e.g. Vanish+Break with not work on an enemy immune to petrify).
Vanish+Doom is the most commonly know way of using the glitch, but other methods do work as well:
- X-Zone (bypasses enemy final attacks)
- Snare (from Rhodox rage or Dusk Requiem dance, bypasses enemy final attacks)
- Odin/Raiden (bypasses enemy final attacks)
- X-Fer (Magitek skillset, bypasses enemy final attacks)
- Strago/Relm Desperation attacks
- Cleave (swd tech 8, bypasses enemy final attacks, not useful in a speedrun)
- Roulette (Hasn’t been tested and isn’t useful in a speedrun)
- Reversing Phantom onto the enemy with Muddle is an alternate way of vanishing the enemy.
Note that while the instant death version of Chainsaw is considered a magic attack, it does not defeat vanished enemies.
Many bosses in FF6 are immune to death, most notably Guardian, Inferno, and the final boss tiers. Slots (JD/RJD) or direct damage are required to defeat them.
While this glitch has been used in the past, all current routes do not make use of it mainly because you skip bosses where it might be useful and Doom requires extra grinding to get it early.