Berserk - Target's attack increases by 50% and is rendered uncontrollable. Target will attack random enemies with physical attacks.

Berserk [!White] - Always Hits.

Beastmaster

World 2, Forest of Moore - Mammon
The Rift, Dimensional Castle - Mammon

White Mage

World 2, Buyable at Moore Village for 6000 gil

Black Mage | Blue Mage | Freelancer | Mime | Red Mage | Summoner | Time Mage

World 3, Wonder Rod

Moon Flute [!Blue] - Always Hits. Only targets party.

 Blue Mage

World 1, Walse Castle - Jackanapes (Counter to HP damage)
World 1, Ancient Library - Page 256
World 2, Exdeath's Castle - Jackanapes (Counter to HP damage)
World 3, Overworld (Moore Town, Surgate, Mirage areas) - Mykale 

Blessed Kiss [!Mix] - Always Hits. Bypasses Berserk immunity. Adds Image and Haste.

Chemist

Mix Maiden's Kiss + Holy Water 

Bacchus's Cider [!Mix] - Always Hits.

Chemist

Mix Holy Water + Turtle Shell

Power Staff [Weapon] - Attack proc. Always Hits.

Chemist | Freelancer | Mime | Red Mage | Time Mage | White Mage

World 2, Exdeath's Castle - Black Warlock (Rare Drop)

Berserk [Passive Ability] - Only affects characters equipped with ability.

Berserker

Always in effect.
100 total AP. L1 ability. (Other jobs)