Quite good deck for being new to EDH.

Here are some things I saw:

Cut out Stormscape Familiar . It is too unstable in a all color highlander and doesn't lessen the mana costs of your commander (and because of the rulings it can't lessen the extra costs for being cast again from the command zone).

Replace Jace, Architect of Thought with Jace Beleren for more efficiency and better card draw.

Replace Mass Hysteria with Fervor or Fires of Yavimaya so you don't boost your opponents.

Cut out lands that come into play tapped like Seaside Citadel , card:Dromar's Cavern and Izzet Guildgate . They only slow you down for coming into play tapped. And cut out Riftstone Portal since it won't hit the graveyard most of the times since land destruction is the most uncommon effect in EDH and if a player does use those effects he won't target this land and simply every other land you have.

For a good mana base example you can visit a deck a friend of mine made:

Overlordy and his Minions

It has proven to be extremely efficient.

Cut out Chromatic Sphere , Obelisk of Grixis and Obelisk of Bant . They are too inefficient. Include Coalition Relic , Gilded Lotus , Sol Ring and Thran Dynamo instead if you want more ramp in here. Artifacts like Rakdos Keyrune (I know you already have it in here) and Rakdos Signet are better then those Obelisks or the Sphere too.

Cabal Ritual and Dark Ritual are mostly pretty inefficient in EDH. Cut those out. They are too instable too since you require black mana AND only get the mana 1 time. Mana artifacts or ramp cards that get you lands into play are more efficient for being more constant in giving you mana.

card:Archangel's Light is pretty mana intensive. Only use it if it is really worth it.

Fiery Gambit is funny but a simple burn spell would be more efficient. If you just play it because you like it keep it. ;-)

Journey of Discovery and Reap and Sow are good but I would suggest to add less mana intensive ramp spells to get more speed earlyer. Cultivate , card:Kodama's Reach and card:Nature's Lore (to get duals like Temple Garden out) would be good options.

MartialArt: Thank you! I'll definitely consider all of your suggestions! I think I'll keep Mass Hysteria , at least for a little while, as I think the whole game might be funnier if all creatures in the game had haste. If it turns out to be a drag after some playtesting, I'll cut it for Fervor . Great feedback, and again, thanks!

I would Recommend Keiga, the Tide Star as he works well with Scion. Teneb, the Harvester Also works well as recursion, and you can use his ability with Scion. Yore-Tiller Nephilim and Charnelhoard Wurm aren't dragons, but they're good rucursion.

In general, Wrath effects are good in EDH. In the vein of MartialArt's comment, I would suggest replacing Dark Ritual and Cabal Ritual for Wrath of God and/or Damnation and/or Final Judgement . Also, I would suggest -1 Chromatic Sphere and +1 Spell Crumple .

5 Colors.... ouch. How about Chromatic Lantern and card:Dawn's Reflection

Come to think of it, Chrome Mox would be a great addition to this deck!

Where is Tom Cruise?

RousseausDisciple: Yeah, I'll probably get a board wipe or two.

Ferus_vir: Yeah, I'm considering getting another Chromatic Lantern . Didn't know about card:Dawn's Reflection, but I'll think about acquiring it. Until then, I'll probably use Abundant Growth .

MinscAndBoo: I'm sorry, what?

I would rather include Trace of Abundance then card:Dawn's Reflection for more safety and more speed (since it can get out 2 turns before card:Dawn's Reflection).

I like the deck. Just one idea with using Scion.

Have you considered the Vorosh/Skithiryx combo?

Scion into Vorosh for the six +1/+1 counters, you have a 10/10. Then drop into Skithiryx and punch in for a insta-kill if you can make Scion unblockable or they can't block..

It may be one player only, but it still leaves you with a 10/10 and one dead player.

+1 for this though! =D

TheKrazy001: Oooh.

dnoate: Yeah - it's very fun, and it can help eliminate the pesky control players or other larger threats VERY quickly. Definitely a fun combo I've enjoyed pulling off.

Elvish Piper or Quicksilver Amulet ?

@sheamagic: Quicksilver Amulet 's already there, if you look closely. ;)

It was hiding.

@sheamagic: That pesky, sneaky, up-to-no-good Amulet.