Inflict a single character with every status ailment throughout the course of the game. It does not have to be done simultaneously.
Here is a list of the effects and ways to self-inflict them at endgame. If waiting until endgame, it's likely you'll have been hit by most of them already. Zidane is a good choice as he'll have been in your party for the majority of the game.
Beneficial Effects
Auto-Life: Amarant's Aura, Quina's Auto-Life (Cerberus @ Ipsen Castle), support ability
Float: Dagger or Eiko's WHM, support ability
Haste: Eiko's WHM, support ability
Protect: Dagger or Eiko's WHM, Quina's Mighty Guard (Gargoyle @ Ipsen Castle)
Reflect: Dagger or Eiko's WHM, Eiko's Carbuncle, support ability
Regen: Eiko's WHM, support ability
Shell: Dagger or Eiko's WHM, Quina's Mighty Guard
Vanish: Quina's Vanish (Hornet @ Gizamaluke's Grotto)
Detrimental Effects
Berserk: Dagger's WHM
Confuse: Dagger's WHM
Darkness: Dagger's WHM
Doom: Quina's Doom (Veteran @ Ipsen Castle/Memoria, Ash @ Memoria)
Freeze: Steiner's Ice Brand with Add Status, Quina's Frost (Wraith @ Mount Gulug, Chimera @ Memoria)
Gradual Petrify: Basilisk @ Burmecia, Gargoyle @ Ipsen Castle
Heat: Steiner's Flame Saber with Add Status, Quina's Mustard Bomb (Grenade @ Mount Gulug)
Mini: Dagger or Eiko's WHM
Petrify: Vivi's BLM
Poison: Vivi's BLM
Silence: Dagger or Eiko's WHM
Sleep: Vivi's BLM, Quina's Night
Slow: Vivi's BLM
Stop: Vivi's BLM
Trouble: Zidane's Annoy
Venom: Whale Zombie (Most beaches)
Virus: Yan @ Vile Island
Zombie: Whale Zombie (Most beaches)