Hearthpwn

Why play this deck?
Because evolve is a fun mechanic and especially with nerubian prophets and the like is really powerful as well.

The awesome combo:
2x 0-mana Nerubian Prophet+2x 0-mana Thing from below+2xMaster of evolution+2xEvolve.
That gives you 40 mana worth of minions for 10 mana
If you get reductions you can also play brann in the combo to get even more EVOLUTION.

How to play the deck: 
Try to not completely lose board control, but don't waste important cards (like nerubian prophet) to get it.
Play card draw to draw nerubian prophets sooner and totems to reduce thing from below's cost.
Use jeweled scarab to get board clears, hex or other powerful cards. Sometimes a taunt or random totem/removal is the best you can get.
Onyxia synergizes with a lot of the deck:
                     -Onyxia+Evolve = 10-drop + 6x 2-drop. Could spawn doomsayer if unlucky.
                     -Onyxia + Wait a turn + Bloodlust = 35 damage.
                     -Welps+Flametongue totem = Stronk.
Be careful when evolving. 7-mana can be Acidmaw, 8-mana can be anomalus and ofc. 2- mana can be doomsayer.
Brann bronzebeard works really well with master of evolution.
Azure drakes can help buff your lightning storms.
Flametongue synergizes well with bilefin and Feral spirits.
When you have Bloodlust, you can try to push for a big board and get lethal.
Almost all minions in the deck have battlecries and thus can be good evolve targets.

Mulligan: Keep 2-mana stuff and Nerubian prophet.
Further just mulligan as much away as possible to draw nerubian prophets.

Additions: Elemental destruction for more boardclear.
Second fire elemental.
Second scarab for more flexibility. (It can often get single target or aoe removal.)
Second Novice engineer/Gnomish inventor for more draw.
Second bilefin for more early game pressure.
Maybe Totem golem, but it synergizes badly with evolve.