TANK stacking

[Xenosan]

besides the LB, some jobs work against each other, when you bring 2 of them. in regards of tanks having 2 Dark Knights in the party basically removes the utility a DRK offtank offers, since using The Blackest Night on the DRK maintank is counter productive. i don't know if you can overwrite his shield, but when the MT uses it on himself he gets a 20% shield, if the OT uses it on the MT it's only a 10% shield.

If you TBN a DRK who already casted it on themselves yours just doesn't take effect (like if you Esuna someone who has no ailments "XXX has no effect").

Not sure what happens in the opposite, I assume you do overwrite theirs because I don't recall ever seeing a 'TBN has no effect' using it on myself while tanking, DRK/DRK'd plenty PUGs so imagine I would have seen it if that were the case, but I'm not sure