doctorhydrogen

Galvanoth would give you a second Melek-like ability. Hypersonic Dragon seems useful, too.

Augur of Bolas, Djin Illuminatus, Dualcaster Mage, Goblin Electromancer, and Nucklavee might have roles. You could pick them up when you order the deck since I think all are cheap just in case you want to make changes later.

You could also consider replacing Fog with Constant Mists. Worst case it's a Gog that costs one more to cast, but late game (which is when you're probably casting Fog) being able to buy it back for a turn or three or four can be back-breaking for someone. There have been games where people have flat-out scooped to Constant Mists because they know they won't be dealing damage for 3-4 turns during which time I'll win.

Swap Naturalize for Deglamer or Unravel the Aether. You don't want to be holding a Naturalize in hand while starting at a Blightsteel Colossus or something wearing a Darksteel Plate or a token deck about to drop 20 tokens with Purphoros online. Plus stuff is harder to get back from the library than the graveyard, and it prevents death triggers. I've never looked at a Deglamer in my hand and wished it was a Naturalize, but there have been hundreds of times I've been holding a Deglamer and been glad it wasn't a Naturalize.

It's kind of a jerk card, but Hall of Gemstone is brutal in mono-green, as is Primal Order.

I've been running +1/+1 counters for awhile, first as Voros, then Mimeoplasm, then switching to Jenara, now back to Mimeoplasm. Jenara just never quite felt as strong as Mimeo, though I can't exactly put my finger on why. That said:

Azban Falconer did good work. SURPRISE ALL MY DUDES HAVE FLYING can really change the fight in a hurry.

Greater Good was probably the strongest card in the deck since so many of my guys tended to be huge. Even if you don't use it for any other reason that to sacc dudes someone targeted with removal or after a board wipe it's a beast.

Solidarity of Heroes kills people, flat out.

In a two color deck you could drop to 38 lands with no problem, especially in a deck with decent draw options. I only run 36 in most of my two colors.

If you really want to stay at 39 I'd pull Thought Reflection. It's a great card on paper but in reality 8 mana is a whole lot to spend on a spell that probably won't do anything until your next turn.

If you decide to go the land route I'd still pull Thought Reflection and replace it with Recurring Insight. RI will cost two less to cast, gets you multiple cards immediately instead of having to wait a few turns to pay off, doesn't risk being disenchanted before it can do anything, and can be copied in this deck. Generally it gets you a LOT of cards. It's my absolute favorite big draw spell in blue.

It's probably not going to make much difference very often, imo.

Ponder is probably better in that same slot than Serum Visions. There's a reason it's banned in Modern and Serum Visions is not.

It's like three bucks, but Pyromancer's Goggles would be nuts in this deck.

My only word of caution if this is a deck you don't currently have and are working on is that Merieke can generate really boring game states. I wound up dismantling mine because pretty quickly it became obvious that the best way to deal with her was to not play stuff until someone else had a juicy target out first. Games wound up being draw-go for an hour while people fucked about on their phones because nobody wanted to lose things. Then someone finds a combo piece and auto-wins. The combo guys loved me for making everyone else not play stuff, but everyone else hated it because long-ass games where people didn't do much aren't terribly exciting.

I'd also consider finding a slot for Homeward Path. I don't think every deck needs one necessarily, but it's really useful in a Voltron deck where you have to worry about someone stealing your dude wearing six swords or whatever.

Cathars' Crusade gets way out of hand in a token deck like this.

I'd also consider Druid's Repository. The mana it can generate is insane.

Guided Passage is the best card to run in Riku. Absolute worst case it gets you the three worst cards in your deck for three mana, and if you're building right the three worst cards should still be pretty damn good. Copying it gets you six. Plus the look on people's faces because they've never heard of it is priceless.

I'd replace Disenchant with either Revoke Existence (same cmc but a sorcery), Fate Forgotten (one more to cast but instant) or Return to Dust (two to cast but can hit two targets). You don't want to be holding a Disenchant and starting at a Blightsteel Colossus or Darksteel Plate on a dude you need to kill or a Theros god about to ruin your day, and you want to prevent graveyard triggers or Wurmcoil Engine splits or people reanimating stuff or getting it back. It's well worth running one of those three over Disenchant to be able to exile. I've never once thought "man, I wish this was a Disenchant so I could save a single mana" as I started at my Fate Forgotten, but there's a billion times where I've looked at my Return to Dust and Fate Forgotten and be glad as hell it wasn't a Disenchant.

Flickering Ward is a decent card in general, but in a deck like this where you get benefit from bouncing it over and over like a fool it would be great. I sometimes draw a dozen cards a turn off it in my Sigarda enchantress deck.

Honestly, Diabolic Tutor is a better than Beseech the Queen. Absolutely best case Beseech costs BBB vs BB2, so to save one single mana it becomes harder to cast, you're restricted to the size of the card's cmc, AND you have to reveal what it is. There's almost no situation saving one mana (best case if you have BBB free mind you) where that is better than having no restrictions and keeping info on what you tutored for to yourself.

Angel of the Dire Hour would be good here.

Siren's Song might work and is on theme.

Rhystic Study (or Mystic Remora or even Honden of Seeing Winds) would probably draw more cards without spending mana or revealing cards than Illuminated Folio. I'd run Recurring Insight over it, too.

Sun Droplet has worked nice so far letting you get random life gains (and therefore counters) at weird times when you normally wouldn't get any.

Pull Damnation, trade it for some other awesome 50 dollar card, and run Wrath of God for a buck, and rejoice that you noticed zero difference in the trade out while at the same time picking up a 50 dollar card :)

Yep. It even works if the effect is already in place, too. So even if they have any card placed in the graveyard get exiled you can still make it work. The only way to really lock the ability out is to prevent library searching.

Good luck with it!

Also just so you know Scion's ability works even if the creature doesn't go to the graveyard. So if someone has a Rest in Peace or Leyline of the Void or whatever in play, you can still make Scion become a copy of the dragon. All that matters is you attempt to put the card in the graveyard. If a replacement effect exiles it it doesn't matter as you've fulfilled all the steps you were obligated to attempt to fulfill. It might never come up, but my meta runs a lot of graveyard hate and my friend has had it pop up on a few occasions:

http://www.mtgsalvation.com/forums/magic-fundamentals/magic-rulings/magic-rulings-archives/528272-scion-of-the-ur-dragon-rest-in-peace

I think you should add it. I ran Atarka dragons for awhile, and it takes the sting off a Doom Blade or something when you can draw 6 cards off it, or 18 off a board wipe, etc. Maybe in the place of one of the weaker dragons?

Also, Hero's Downfall does the same work as Ruinous Path at instant speed. Instant seems more useful than Awaken on a sorcery.

Wear and Tear is useful, but in a format with Theros gods and Blightsteel Colossus and Darksteel whatever I'd be tempted to run Return to Dust in that slot. One mana more but you have the flexibility to hit two artifacts or two enchantments if need be, and it's an exile effect so you can hit indestructible stuff and it prevents graveyard recursion.

I highly doubt in the average game Training Grounds will save close to as much mana as Sol Ring would generate. I have a friend running a similar version and he ran a test where every time Training Grounds was out and he utilized the ability would he be better off with Fellwar Stone, and after something like 20 games he said Fellwar generated considerably more mana than Training Grounds saved. Given that Sol Ring is quite a bit better than Training Grounds I'd say it's doubly true. It's fairly easy to test, though. Do the same mental game, and whenever you drop a Training Grounds on every turn ask if you'd get more benefit from a Sol Ring. I'd wager 90% of the time the answer is yes.

No room for Greater Good? Even if you never use it besides in response to a board wipe or targeted removal it almost always is a bomb in a deck with this many fat-ass creatures.

Command Tower and Exotic Orchard would be great lands here.

Clone Legion never seemed to work for me. If there are enough dudes out to have it be worth while all you do is generate a stalemate unless you plan to Rift next turn or something. For that much mana a card should blow out or something. In this deck I'd just run Insurrection. Why Clone Legion a bunch of dudes you can't do anything with for a full turn and even then they'll be facing blockers when you can just take everything and probably kill someone with it?

The exception might be in some kind of theft/reanimator deck where you make the clones to sacc to something to procc Grave Pact or whatever, but even then I think I'd still rather run Insurrection (or a Plague Wind-type effect, etc.). Clone Legion just requires too many moving parts to come together simultaneously in order to generate a win.