Zalabar the Dark Tinkerer
This guy's a brutal game-finisher, if you've got the right deck to support him. When the fight's been dragging out and both sides have a healthy-sized graveyard, this little gnome'll come in and win the game for you almost single-handedly. The health point swing between your hero and your opponent's is doubled with the healing power, and his Elusive trait means he can't be attacked by enemy allies or heroes. Only abilities can hit him and he's got the health pool to take a few hits before going down.