This deck needs MOAR aura's... I call for viperesque to make some suggestions (his Uril deck is... STRONG). Cards like Battle Mastery and Ancestral Mask are auto includes.
Pyroclasm and Volcanic Fallout don't hit enough things to be playable. Moonhold, Silence, Orim's Chant and Abeyence are just bad in this format because they only hit 1 player for one turn in a multiplayer game, which is doesn't do anything...
Please cut Carnage Alter that card's the worst. Not only does it not do anything... it costs mana as a sac outlet. You should play either Phyrexian Alter or Greater Gargadon instead. You should probably be Playing Greater Gargadon anyway.
Protean Hulk is banned. Squall line doesn't do enough. Nevinyrral's Disk and Oblivion Stone are both a million times better. Both snake Umbra and Grappling Hook do absolutely nothing.
Braid of Fire does nothing because it adds mana in the upkeep. Crucible of Fire is the worst topdeck post Wrath of God and it's unnecesary because your guys are big enough anyway. Targetted removal doesn't see enough play to make Asceticism at all playable, and it's really bad vs Wrath effects that all say "cannot be regenerated", which is all of the playable ones. Rancor doesn't do enough to deserve a slot in this list. Also you need to upgrade your dudes. Try looking through gatherer (gatherer.wizards.com) and filter for creature type dragon. I would suggest Dragon Tyrant, Dragon Mage and, if you gan get your hands on one, Thunder Dragon. Also, you might be able to get away with running Semblance Anvil.
This deck needs MOAR Teferi's Puzzle Box, Wheel of Fortune, Maggus of the Jar, Memory Jar, Wheel of Fate, Windfall, Timespiral, Timetwister (if you can get on or just proxy). Those cards are all really sick with Niv Mizzet.
I would cut the Eldrazi Conscription. It's the worst topdeck when you're behind, and in the midgame you'd rather be casting a fatty. Your deck seems pretty weak to wrath effects, so I would consider Symbiotic Wurm. Also Birds of Paridise seems really underwhelming, it's also the worst topdeck when you're behind, and in the early game I don't think it has enough of an impact on the game state. I don't think Mage Slayer is good enough. Like I said to Eldrazi Conscription, you'd rather just be casting a fatty. I would suggest going to some of the older sets for imspiriation for upgrading you're fatties aswell. Cards such as Dragon Mage and Dragon Tyrant have a place here. Other than that the deck seems fine.
El Taco the Rogue - Memory Jar is for when you run out of gas. Say you have 2 cards in your hand that do nothing and a Jar in play. You sac the Jar in your upkeep, then draw a card for your turn. Now you have 8 cards to play with. Also, it doesn't need to be used in a combo to be good.
http://forums.mtgsalvation.com/showthread.php?t=104356
This deck needs MOAR Teferi's Puzzle Box, Wheel of Fortune, Maggus of the Jar, Memory Jar, Wheel of Fate, Windfall, Timespiral, Timetwister (if you can get on or just proxy). Those cards are all really sick with Niv Mizzet.
El Taco the Rogue - Memory Jar is for when you run out of gas. Say you have 2 cards in your hand that do nothing and a Jar in play. You sac the Jar in your upkeep, then draw a card for your turn. Now you have 8 cards to play with. Also, it doesn't need to be used in a combo to be good.