Have you thought of swapping out Evolutionary Leap for Retreat to Kazandu? Also, perhaps add some Gleam of Authority?

Yes, I am definitely considering adding Retreat to Kazandu. I will probably pick a couple up at release and try them out to see how they go.

The problem I have with Retreat to Kazandu is that it's slow for what this deck wants to do. What I'm getting at is that it competes with 4+ other cards on turn 3. Would you rather play that or:

Deathmist Raptor, Undergrowth Champion, Managorger Hydra, Den Protector face down, Avatar of the Resolute...

Basically to me and during testing, it felt like a dead card because during play it doesn't feel like it's on curve. You're not doing anything to move the game forward on turn 3 by dropping that card because it requires landfall to do anything. This is actually the most common problem people have with Hardened Scales. You drop it on turn 1 (preferably) and it doesn't do anything. However a 1 mana do nothing on its own card isn't too bad, a 3 mana one however is problematic when you're playing a deck that needs to move fast.

I would think that taking it out and putting in something like Abzan Falconer in order to give your entire team flying for the win would be better. Or Lantern Scout to give your entire team lifelink for a turn. Anyway maybe I just never got the value out of it.

I think you should really consider abzan falconer for this deck. I've been running a lot of gw counters lately and when you just suddenly make all your guys fliers with a 3 drop, the game can really start to tilt in your favor.

As for the retreat, I'd recommend citidel seidge. One more mana and you get and extra counter or tap down one of their creatures each turn, which is just a lot more value in my opinion.

Digging the rest though B)

Also Rot Shambler is a thing. Adding 2 in place of the Raptor.

I highly recommend Abzan Falconer for this deck. Play him late game after your opponent has used up some of their removal. Then, all your creatures become flying bombs.

Ive been building a deck like this for a while and I think cards like Deathmist Raptor and Retreat to Kazandu would be a little to slow although my build has a little more white with cards like Anafenza, Kin-Tree Spirit and Gleam of Authority. Rot Shambler seems like a great adition

This looks really good, I have been testing out a similar deck today. I had huge problems with Abzan Charm hitting, so I think Feat of Resistance seems like a great include, which I am definitely going to swap in.

I do have 2 suggestions I would like to mention, the first is Honored Hierarch. It is great when you can drop a Honored Hierarch turn 1, then a Hardened Scales followed by a Servant of the Scale next turn hitting renown on the Honored Hierarch. Turn 3 attack for 5, then tap the Honored Hierarch to cast Undergrowth Champion before hitting the landfall trigger.

The second card is Inspiring Call, works great to protect from board wipe spells and refuels your hand quite rapidly.