This deck plays much like the old Prince Keleseth Zoo from KotfT.  There have been some updates to it that help it go quickly though.  

Obviously, if you can hard mulligan to get Prince Keleseth in your opening hand, that is ideal. Doing that just sets up a lot of fun stuff that happens and goes straight to face. 

I swapped out the Fungal Enchanters for Potion Vendors because they are 2 less mana.  With The Soularium, that comes in handy.  Also, putting in the Power Overwhelming can put a serious stop in most opponent's plans.  Making a Doomguard slap to the face for 9 that much more scary. 

My happiest update to this deck though has to go to Frenzied Felwing.  It's Happy Ghoul's distant cousin that works so wonderfully in this aggro deck.  I've been able to drop him as a 4/4 along with Lightwarden and heal and have 10+ damage on the 3rd turn.

As with any aggro deck, the downside is going to be Big Priest.  I've yet to beat it.  With so much removal and taunt, it's the WORST match up.  Surprisingly enough though, with the threat of Cyclone Mage getting hit, people are playing that and Highlander Mage.  Which, aggro should totally just toast.

I kept Bloodreaver Gul'dan in there solely for times when the games happens to go passed the 6th turn and you have seen a number of your demons drop, it's a good 3 lifestealing damage for the hero power, along with bringing back some Doomguard happiness. 

I have been playing around with Zilliax, because he gives the little health restore effect for Lightwarden and Happy Ghoul, but I think he may just be a little too slow when an Ironbeak Owl will get that nasty taunt out of the way to go face with your other stuff easier.  

Anyway, enjoy and have fun!

***UPDATE I have removed Zilliax and put in the Ironbeak Owl.  I was right in thinking that the Big "Z" was a little too slow for the deck and having the silence to break passed that one taunt getting in the way of going face was the better option.   If you are seeing aggro to aggro a lot, Big "Z" is the way to go since it stops up to 2 attacks, and gives you back some life that you can Life Tap.  Other than that, I'm rocking the night owl.