Never done a raid, but "He Who Has No Life" would practically beat some MC bosses single-handedly no?
My idea for a raid is really an idea I had for a priest deck, but it just didn't work when I couldn't get multiple copies of Donna Calister in play. With 3 players sporting 4 copies of Donna Calister each though Lightwell just becomes a bomb card. Two Donna Calisters with Lightwell can take down an infinite number of attacking Onyxia whelps for example. Sarmoth and Acolyte Demia as well as non-attacking heroes can also combo with Lightwell decently. A warlock with Fel Armor out would regenerate 4 every turn for free. A warlock can also pump out the AoE damage in case the opponent just decides to amass an army till they can punch a hole with abilities so they're a clear choice as the 2nd hero. (Those same two Donnas would only be able to kill 4 whelps every 3 turns on offense for example.) The 3rd hero should probably just be any hero that can pump out single-target damage.