Slow - Reduces rate of ATB gauge by half.

Slow [!Time] - 95% Hit Rate.

Time Mage

World 1, Walse, Karnak, Istory for 80 gil

Slow 2 [!Time] - 80% Hit Rate. Targets all enemies.

Time Mage

World 2, Regole, Bal Castle, Quelb, Surgate, Moore for 3000 gil

Web [Enemy Spell] - 99% Hit Rate.

Beastmaster

World 2, Exdeath's Castle - Tarantula
World 3, Overworld (Moore Area) - Gloom Widow

Slimer [Enemy Spell] - 99% Hit Rate. Also inflicts HP Leak.

Beastmaster

World 1, North Mountain - Rock Slug
World 3, Great Sea Trench - Unknown (Spore, first form)

Bindweed [!Gaia] - Always Hits.

Geomancer

Available at L51 in Forest terrains.