Hearthpwn

Just flood the board. Win with first try. Super fast and opponent probably surrenders.

Possible replacements:

Dragon Synergy: Arcane Breath, Firetree Witchdoctor, Blackwing Technician, Scalerider, Blackwing Corruptor (Book Wyrm, Crowd Roaster, Rend Blackhand)

Demon: Light's Champion

Pirate: Parachute Brigand

Elemental: Thunder Lizard (Animated Avalanche, Frost Lich Jaina, Blazecaller)

Mech: Mechwarper, Mimiron's Head, Wargear

Murloc: Coldlight Seer, Murloc Warleader, Felfin Navigator

Beast & Totem: None

would suggest Shaman with:
Everyfin is Awesome, Totemic Surge, Totemic Might, Primal Fusion, Totemic Reflection, Draenei Totemcarver, Thing from Below

Warlock: Demonfire, Bloodfury Potion, Crystalweaver, Demonheart

Warrior: Skybarge

Hunter: Metaltooth Leaper

Generally, everything above 5 mana is too slow, same goes for other discover mechanics, particularly dragon priest.