Zader- can inflict dots, has unlimited dots if he's alive, can pretty much oneshot a non tank with culling blade
IG-88- can do heal immunity, abilty block, and defense down. More importantly gains 20% damage per debuffed enemy, so as soon as Vader goes he's doing double damage
Boba- can inflict dot on basic, dot and abilty block on AoE, special does more damage per status effect
Darth sidious (only with zeta)- heal immunity on basic, can do 2 dots per character with AoE, 4 dots on each crit
Dengar- basic has 60% to call assist when hitting a debuffed enemy (and if boba or 88 are pulled in its the assist is a crit which ig-88 has +45% crit damage on top of his doubled damage), second does speed down and can stun, AoE depending on crits can do tenacity down allowing for more debuffs, dots, and even turn meter removal