Klaue T2 gives allies a 30% crit damage boost.
Beast T2 increases critical rate moderately plus some defensive buffs.
Warwolf can be swapped in to howl then swapped out to carry the attack buff over.
Mantis grants critical damage and ignite defense at T2. Her 5 can be used as a buff to critical rate.
Nadia can shrink an enemy then swap out and grant attack bonus to allies that attack the shrunk enemy.
Cyclops grants bonus energy attack.
Quake can be swapped in then use 3 to buff the next attack by a large %. This carries over to the next attack even after you swap her out (like a guaranteed Dmg proc).
Ancient One grants elemental damage up and ignore dodge.
Weapon Hex’s orb does a small amount of damage and consistent healing.
Ghost grants energy attack (includes bigger boost and adds heroes with uniform).
Ebony Maw with uni increases damage to universals.
Ronan grants dodge ignore.
There are a few others that have non debuff / damage related supports.