Since GAS can be annihilated, this leaves room for theory crafting!
GAS isnt immune to fear (cleanses it though) nor annihilate which leaves a good bit of room for DR.
The team I'm thinking of is, Sith Trio, DR + SiT / GBA.
The pretaunting tank soaks up damage since they cant bypass taunts.
Traya lead will penalize echo & ahsoka for attacking out of turn.
Sion will inflict pain on enemies & can remove any buffs.
Nihilius is there for annihilate
DR is there to spread fear to the whole team as nowhere in GAS' kit says allies are immune to debuffs.
Now GAS' kit says allies cant loose health but that doesn't mean they're immune to debuffs or buff removals.
(Have to test to see if my hypothesis is true or not)
The gameplan is simple, spread fear & pain while Sit or GBA soaks up damage then lead up with Nihilus' drain ability.
Save Trayas isolate for once GAS is down and isolate the biggest nuisance on the team.
Nihilus should have annihilate ready so at this point wait until you can kill off GAS by weaking 5555s & others.
Annihilate GAS then 5555s then party because that's game.
(Obviously this has to be tested but it's the best I got)
What are your guys' theorycrafting counter(s)?