Just thinking about how they could rejuvenate older allies who don't have passives. Simply give them a passive to grant a random shield or beneficial effect to all allies for 1 turn with perfect/basic attacks.This would make older allies that had descent abilities now have some value in the current game structures. Not sure how much effort is involved in adding passives to allies who don't have one but it would help diversify the game while not taking anything away from newer allies being released.

Assassin Corrupt Droid could grant Physical Damage shield to random/all allies for 1 turn on perfect/basic attacks.

Sentinel Souless Demon could grant Ascension for 1 turn to random/all allies for 1 turn on perfect/basic attacks.

Nothing too fancy but enough to make some less used allies a consideration.

Just thoughts.