Make a small change that would break a class completely.

[Gilraen]

Gladiator - Flash has it's enmity effect removed, instead it's blind effect is made native and is increased to 100% miss chance.
Thaumaturge - Swiftcast inflicts a 10s Slow effect once expended.
Conjurer - Protect and Stoneskin can no longer be cast under aggro.

Append:
Lancer - Invigorate converts MP to TP at a rate of 3:1, 4:1 cross-class.
Pugilist - Second Wind converts MP to HP at a rate of 3:1, 4:1 cross-class.
Archer - Barrage is a stance that forces you to stand still during attacks as well as impose a slight penalty to accuracy.