These specific character skills do 25% less damage while in the back row.

Cloud - Limit:
Braver
Climhazzard
Omnislash
Omnislash V5

Ronan - Combo
Fists of Thunder
Aura Blast
Crippling Strike
Hundred Fists

Tifa - Reels
Waterkick
Beat Rush

Magitek:
Magma Beam
Frozen Beam
Thunder Beam