88 lead causes DoT for each crit and can do abilty block and defence down
Vader to add more debuffs and his culling blade to get insane numbers
Tusken shaman (if you can get him) can do DoTs with his basic and his heal is more effective for each enemy suffering a negative effect
Phasma can do speed down and can give advantage to help counter the often low damage of AoEs
lando's if it gets two crits will reset the cooldown and do more damage next time
B2 (again if you can get him) can dispel all positive effects, inflict buff immunity and with his unique will be going fairly often
And the last one I can think of is HK since if his grenade is omega'd will have a 25% (50 Against Jedi) each to do 5 different debuffs
So basically if your F2P 88 lead, Vader, HK, phasma, and lando. If you have them I'd probably swap lando out for B2 and HK or shaman