I've been toying with GU Splinterfright for some time now and, despite loving it, I am not completely sold on it. The biggest issue it has from my experience is its inconsistency like drawing a lot of Splinterfrights and Wurms but few enablers or vice-versa. Another lesser problem but one that comes far more frequently that i'd like it to is when you mill that necessary 3rd or 4th land or when Tracker's Instincts reveals 1 or 0 creatures (for fuck's sake). Sometimes it goes off like a fusion bomb but it often crashes to the ground miserably. Here's a rough list from memory:


Some cards might require explanations:

Ponder over Thought Scour. Like I said the deck is inconsistent and Ponder trades the potential turn 2 Wurm for draw-smoothing.

Merfolk Looter over Deranged Assistant. Frankly, I don't like the assistant. Accelerating is cool, sure, but I preffer the greater consistency of drawing one and choosing what goes to the bin. It sucks to have Grudge/Rites in the openihng hand and Looter gives me a way around that.

Mana Leak/Negate. Day of Judgement and Primeval Titan just never see it coming.

Phantasmal Image. Between being Splinterfright 5-6 and copying Adepts, Geists, Aberrations, Saints, Robots, Titans and Wurmcoils, he's incredible. Sometimes I wish he was Body Double though.

Surgical Extraction/Purify the Grave. Should be there somewhere but aren't for some reason. Purify is nice for having Flashback so I don't terribly mind milling it.

If I get a good draw (not god, just good), I can fight very deck in the format but that doesn't happen very often.

Then I thought of a RG version of it. Still haven't figured out the numbers.


The plan is to have Vexing Devil on turn one and it is sacrificed, turn two Wurm and Loot or Track from there. Faithless Looting may be even better than Ponder or Thought Scour because I select what is discarded and it has Flashback. Also Red means I can use random burn if I want and makes Ancient Grudge in color. Other cards that might be good are Huntmaster of the Fells because he is good period and Ray of Revelation when Scars is out.

Ok, I'm pretty sure I see your problem(s).
First off, I actually cringed when I saw all five types of basic lands in a pool of 21. It's just not needed, and makes your mana base way too inconsistent. You're making a UG deck, stick to Blue and Green for Arceus's sake. In straight UG, the only land's this deck needs are the Hinterland Harbors, Islands, and Forests. I'd also bump up to 22 or 23 lands, to keep the mana flowing around you milling yourself.
Second, in order for this deck to succeed, you need to seriously commit to milling yourself stupid. The control elements and mana dorks really need to be escorted to the door. Now, other stuff you need can get in without the local Fire Marshal getting upset.
Speaking of stuff you need, Forbidden Alchemy. True, in the mana base outlined in part 1, you can't hit the flashback on it. However, in my opinion, the seven mana for its flashback isn't something this deck can really afford. By the time you hit seven mana, you should be in full attack mode. Also, even without the flashback, Alchemy is fantastic for this deck. Grab the Splinterfright, and get another creature or two into the grave with the same card on your opponent's end step.
Still talking about stuff you need, Thought Scour. With your deck as it was, I understand the switch to Ponder. As you streamline it, Thought Scour really does work for this deck. On a similar note, Dream Twist also really wants a couple copies in here.
Ok, with the changes I have thus far suggested, and some tweaking of numbers, we come out to 56 cards. In case you're interested, here's the updated list I came up with:



Some more tweaking and this can be a 60 card deck, no issue. However, in my browsing of card lists writing this, I found a couple pieces of tech that, if I were to run the deck, I would include. Totally your call, as they're more on the odd side.
First up, Curse of the Bloody Tome. Cast on yourself, of course. Splinterfright's secondary ability can do some work, so why not put some more copies of it into the deck?
Secondly, Increasing Confusion. Can be cast on yourself for fairly efficient milling, especially from your hand. However, in a long, drawn out game, a pair of them can pretty much be an alternate win condition. Tapping out to cast Increasing Confusion from your graveyard late in the game can do huge things to the size of your opponent's deck.
Well, that's my two cents. Here's the final decklist:



As for the RG version, I haven't really looked at it yet. I'll probably be bored later and break it down as well.