MrBarrelRoll

Maybe also try some Tims, like Prodigial Pyromancer or, better, Cunning Sparkmage.

Instead of Demolish, I would recommend Splinter Twin.

That and Acidic Slime is GNARLY.

Would also let you make hasty copies of Primeval Titan so you can tutor 4 lands each turn, which also makes me highly recommend a few Valakuts as well.

If you like the Pyromancer then you'll love Cunning Sparkmage.

Highly recommend you replace all 4.

The Aria is just too slow for you not to run removal, or at least responses. I would add:
O-Rings and Lightning Bolts for removal
Vines of Vastwood as a response

If you can get your hands on them, Knights of the Reliquary are fantastic in a deck like this. They would let you tutor for other lands with "Enter the Battlefield" effects at instant speed, which you can then bounce indefinitely with Ruin Ghost.

I run a G/W deck that has a single Halimar Depths and a single Bojuka Bog, for this very reason. Other good candidates are Piranha Marsh for direct life loss and Teetering Peeks to make creatures huge.

Needs moar Goblin Bushwhacker

And I personally prefer Vines of Vastwood to Giant Growth, but that's just me.

Definitely would agree with Wall of Omens if this was to be made into a 1v1-centered deck.

Also perhaps some Everflowing Chalices, they would give you some much needed mana accel early in the game and would let you level up your transcendent masters faster in the late game. Again not mythic but still quite useful.

That Mana Curve makes my head hurt. How do you plan on actually playing anything??? 4 Cultivates and 4 Growth Spasms aren't enough accel for having 8 cards that cost 8 mana apiece.

Losing the Verdant Forces for perhaps Lotus Cobras or Birds of Paradise would help immensely.

More useful than Progenitus would be Iona I think, to lock down your opponents just a little bit more.

My only worry is that with the Ripple 4 you might get out additional copies of Mortal Combat, in which case you would win multiple games at the same time, causing the fabric of space-time to rip apart, catapulting yourself into a dark land of unknown horrors and also NO CHEESECAKE because in the Plane of Unspeakable Evil it hasn't been invented yet and it never will be.

WHICH SUCKS CAUSE I LIKE CHEESECAKE.

Mitotic Ooze, Mortician Beetle, and Pawn of Ulamog have awesome synergy with a deck like this.

And I might have to recommend Bloodthrone Vampire as a sacrificing engine simply because it's one mana cheaper.

@Zanmor Short answer, yes. You can target as many times as you want, which is why this combo works.

Another idea is Condemn, easy 1-mana way to gain a ton of life, just attack with your creature that has 9001 toughness.

With the plus side that it doubles as spot removal versus your opponent's creatures. Yay versatility! :D

If you want to be truly evil, you know what would be a better endgame bomb than Malfegor?

Butcher of Malakir.

FUN FUN FUN, love it!

Maybe add some Sculpting Steels to make even more Krark's Thumbs?

Also, if you can find them, Mana Crypt for awesome amounts of mana accel that goes right along with this deck.

Last idea: Splash Blue and run Stitch in Time.

Definitely use Thrumming Stone over Wild Pair, generally you can puke all your rats onto the field at once.

And then in case of Maelstrom Pulses or boardwipes, run Mortal Combat to win anyways! Or for even more epic lulz, run Maelstrom Pulse yourself, blast all your rats, and win that way, for one of the most confusing win conditions OF ALL TIME.

For the hilarity factor, Coat of Arms might be more fun than Beastmaster Ascension.

"I have 12 wolves. They are all 13/13."

And then laugh maniacally or something, your call.

I don't think the Juggernauts and Sword of Vengeance are really needed here. Triskelion with Deathtouch is awesome enough as is, you won't need much more than that to win a game. You'd be better off with more ways to protect that combo, which means more counterspells. I'd recommend Mana Leaks and Negates.

Master of Etherium would be awesome in this deck. Once you play your March with a Lattice already on the field, all of their lands die while all of yours become 1/1s that can power up your Master even more!

Then swarm to win, would be a lot faster a win than trying to turbofog them.

Use either Grave Pact or, if you want standard legality, Butcher of Malakir.

That, Bloodthrone Vampire, and Reassembling Skeleton are the centerpieces of a black control deck I've been testing.

2 of each Eldrazi Legend is dangerous, no need to risk the legend rule foiling your plans.

I would heavily recommend using 1 of each of the 3 legends and also Iona, since she's such a good Morph candidate.

Other than that, why so many other creatures? Seems to me that you're running the odds a little too riskily. No need for actual creatures when you can use Awakening Zones, Khalni Gardens, and Zendikons to make pseudo-creatures that would let you much more easily morph out your big scary fatties.