4Game

Octane: if you double tap revive, he stims the downed player, getting them up instantly for 20 or so seconds (after which they go back down, further reducing their bleed out time, or if they pop a medkit or something they stay up.)This has a cool down of about 1min.

Bangalore has her smoke

Wraith has her portal

Loba has the ability to throw her bracelet just prior to reviving, causing both reviver and downed player to teleport mid revive to another location (suggested by u/newmann19 )

Gibraltar has his quick revive under the dome

Lifetime has her auto revive drone

Crypto could revive a player through his drone but takes longer

Pathfinder could grapple downed players towards him

Watson could give extra shield back upon revive (or give a burst of speed)

Revenant can revive whilst in shadow form

Caustic has his gas

Mirage has his invisibility

Bloodhound can have a swarm of crows embody them while they revive, acting as a 360 shield (50-100 damage) that can give them an extra second or so to get a revive off. This comes at the cost of being easier to spot.

Rampart could give 10 seconds of extra damage post revive

Edit: whilst I don’t think every legend should have one, it’s fun to think about what would be the ability they would get.