Electro

Omega w/ certain attacks

AA granted you land enough neurotoxins

CB with enough furies

BW has a 75% max

GP increases chances up to 100% based on combo

Namor /Bishop/Blade w/ GR according to this thread (i dont have them, cant confirm)

Ebony Maw/Domino/IMIW only on non-contact attacks should theoretically work (havent tried)

Luke Cage (and CM movie to a lesser extent) timed correctly w/ invincible

CM doesnt but she does get additional energy

Void/Quake technically never has to touch anyone

Red Skull (awakened)/Hyperion/Mordo and the 2 Stranges if you could get to special 3s without hitting him

Havok and Invisible Woman i believe can mitigate some of it

Elektra? I think she reduces ability accuracy somehow but not sure

Ghost (awakened) if you can somehow never get hit + build up to special 3 from phasing

Technically anyone with a regen+DoT debuff should be able to survive long enough without having to actually hit him, but arent guaranteed to reduce the damage back

As far as anyone fully immune to energy or damage back from Electro, as in all their attacks dont trigger it....none

EDIT: Oh my bad, you said "hero". I dont have time to re-edit bc comments get locked within 15 mins and theres like 1 min left

Batman05

Blade with ghost rider does a good job

Hedron

Hyperions sp1
Continuously spam sp1 by power gain