Antique healbot + Return friendly minion to hand spare parts is such hax. Easy 16 - 24 hero hp points back in late game.
I just had a game where I made a huge comeback against a mage thanks to this.
Turn 9, I play doctor boom with another minion on the board, the mage responded with Antonaidas and frostbolted the dr boom (I was at 13 hp by this point).
Turn 10 I dropped Malganis and ended the turn. Mage decides to Fireball+ping Malganis and Fireballed Dr Boom, leaving me with 1x Zombie Chow, 2x Boom Bots on the field and at 13 hp still. I had drawn Dark Bomb earlier.
Turn 11, I top decked Healbot. Suicided one Boom Bot into Antonaidas, bomb landed on him and hit for 3 (Antonaidas at 3 hp now). Dark Bomb for the kill on Antonaidas. Earlier on I got the rewind spare part from a the mage's Mechanical Yeti. I play Healbot, rewind and hit face with Chow/Boom Bot.
Next turn the mage plays his second Arcane Intellect and then plays unstable portal, getting...Leeroy from the draw, plays the leeroy, attacks+ping face and uses the stealth spare part. I was back down to 14 hp or so.
Turn 12, I topdeck my second shadowflame, used it on my zombie chow to clear the Leeroy and played Healbot again. The mage had Duplicate up and gets another 2 Leeroy (on top of having one remaining fireball from Antonaidas).
Turn 13, I topdeck my second Belcher and managed to drop the mage to 10~ Hp or so. By this point I had like 21 HP or so and the mage conceded.
That was about the only comeback I could think of against a mech mage, especially since he was pretty much ahead throughout the game (mechwarpered + double blastmage consecutively, getting me down to 13 hp by turn 9). It was pretty brutal.