Hearthpwn

 Empty board. 

Play this. 

Summons Malygos, 2 moonkins, velen, 2 spelleavers or cosmic anomalys, + 1 of the remaining. 

Total of +15 spell damage before velen. 

Play smite with your 1 remaining mana. 

17 damage, plus the velen, so...34 damage. 

You have a 34 damage OTK from an entirely empty board from 2 cards in hand, assuming your 2 major cards (Maly, velen) aren't already drawn, and the rest of your deck is still stacked with +2 damage minions. It's worth noting that you could probbaly achieve a similar effect if one of the minions is a knife juggler. You could even pull off the combo if one or even TWO of the minions is only +1 spell damage (32 or 30 damage total, instead of 34).