I'd had the thought of doing a tribal beast deck when Advocate of the Beast was first spoiled, but the biggest problem is that your #1 option beast is rotating, #goodbyeThragtusk. It MIGHT still be feasible but I don't see where it will be all that competitive, as you're essentially just playing a collection of sub-par creatures that don't normally see play because of a combo with one guy that only equates to adding one counter to a creature per turn (not exactly the scariest thing in the world). Your opponents will likely catch on after the first game and can easily just pick off the Advocates when they hit the field... trust me on this, I tried a similar thing with Slumbering Dragon when M13 hit.
That being said, if you're set on the deck idea, here are some ideas for you.
1) Elvish Mystics - not beasts, but mana rampers to help your curve. Think T2 Advocate, T3 Rumbling Baloth. Then you're at least attacking with a 5/5 on T4. Still not ideal though as you could just CAST a 5/5 Deadbridge Goliath on T3... Also, Reverent Hunter could easily be a 5/5 on T2 in the right build once Theros hits.
2) Species Gorger - you NEED to remove this card. The 6/6 body is attractive, but you HAVE to return a creature to your hand. If the opponent is smart, they clear out your other creatures and you end up just casting and re-casting the gorger (which you really don't want to do, as you'll never be able to attack with him). Again, I had grand ideas for Roaring Primadox in M13 and ran into the same issues.
3) Sapphire Drake - I could see as a 2x or 3x, but at 4x you're really making your curve top heavy. Sure, it will evolve some stuff and give flying, but odds are your creatures are going to be pretty large to start with. The flying strikes me almost like overkill in most cases.
4) Pit Fight - Decent removal, but I would suggest you use Rapid Hybridization instead. It's cheaper, it can remove their major threats and replace them with 3/3s OR in a pinch can be used to upgrade one of your underperforming creatures.
5) Why not go with a full playset of Renegade Krasis?
6) Prime Speaker Zegana? Evolves EVERYTHING and gets you some pretty sick card draw?
7) You don't really have one-drops. This solidifies the need for Elvish Mystic.
8) I would actually suggest using Agoraphobia. It's soft removal that is REALLY versatile for what you're doing. You could either a) use it to negate one of their threats or b) reduce the power of one Renegade Krasis, ensuring that it will evolve no matter what you put onto the field. Best of all, you can use even one copy for both purposes given that you can return it to your hand.
9) Given that you're in blue, you REALLY need some means of generating additional card advantage - whether it be Zameck Guildmage or Fathom Mage either one gives you card draw and some versatility. I would suggest the guildmage as it can both bring things in larger, helping to trigger evolve and guarantee everything has counters, AND it can remove counters from Renegade Krasis letting it evolve.
10) Kalonian Hydra says hello (Expensive, yes. But also perfectly suited for this deck.)
Having said all of this, if Renegade Krasis operates as the central piece behind the counter generation, you NEED to be sure that you have numerous creatures that will evolve it without any added pieces. Rumbling Baloth will trigger it up to two times, Sapphire Drake could up to 3 times... but that's it. Adding Zegana, Agoraphobia, and Zameck Guildmage will go a LONG way toward helping you with this.
Either way, it could be fun. I hope some of this helps. Good luck.