I read your thread about fine tuning the deck.

For a casual decks I would think removing Betrayal is a very bad choice since even at a kitchen table game your opponent could side in one of the following: Wear / Tear, Abrupt Decay, Ancient Grudge, Vindicate, Erase or Demystify. Not to mention it's your only form of draw.

If anything I would remove 1x Propaganda and maybe one copy of Betrayal.

Have you considered Fade Away or Drain Power yet? Drain Power may not actually be that great unless your opponent is just trying to wait it out.

Mana Vapors and Rhystic Study also seem good. Mana Vapors seems particularly good if you have Pendrell Mists out. Mana Short could be good also in combination with the mists (it empties their pool - cast it with the mist trigger on the stack).

I read the update after I commented, I think you should drop Errant Minion for Pendrell Mists.

One more thought, you could also sideboard some copies of Chill for when you're playing against some creature-less (or creature-light) red deck, and Energy Flux vs the artifact decks.

Dropped 2x Guard Gomazoa for 2 more Fog Bank. Also removed 2x Slow Motion for 2x Mana Short.

I want to add 2x more Mana Short and 4x Seizures but I really have no idea what else to trade out for them. This move drops my average CMC and i no longer have 6 drops... what do you guys think I should drop for these cards?

Remove black from this deck.

There are many blue enchantments that cost only 1 U mana that do silly things to lands.

You can also play Boomerang in mono-U.

Blacks here to stay sorry. Im not trying to do silly things with lands m trying to win by making them pay to play

You could splash red for Manabarbs. It gives you the redundancy of War's Toll also.

This is the dirtiest, sneakiest, trickiest deck I've ever seen. It's literally perfect.

Uh, in case they overcome you, wouldn't you like tectonic edge?

Ever thought of the card Sinister Possession?

Also check out Web of Inertia

This deck looks like a blast, you mind if I give it a build and run it. My friends might just hate me for it, But Dimir, who cares. :-)

Im putting together a side board for this deck because mana ramping creatures can get past this deck pretty easy. The side board is going to have, 4x Betrayal, 4x Power Sink, 4x Miscalculation, and 3x Slow Motion. It adds a whole new level of creature and big spell hate that is desperatley needed. Remember the point is to make them tap their land.

Mishra's Helix Deserves a spot in here some where.

Gulf Squid, Turnabout; Winter Orb if you need lock down of some kind

I had a similar deck back in the late 90s - When Rising Waters was a new card... Rising waters and Winter Orb made people sad, but they also allowed them to not untap the lands that damage them, which really slows down your clock.

Mind Over Matter maybe?

Narcolepsy is also a card. It might be better than Errant Minion as it deals with threats, but also synergies with seizures.

Stab Wound or Sinister Possession perhaps?

Maybe Fatestitcher to tap your opponent lands.

Add some Enchantment Alteration. If they lay down a Paralyze (which would be good for this deck as well) or the like you can switch it or you can switch your hurt land enchantments on the instant speed. I'm also thinking Hymn to Tourach to disrupt their hand economy as a sideboard. I would suggest a Spellskite to crush burn since that seems to be your one big weakness now.
Panoptic Mirror for the Mana Short. Rhystic Study fits into this deck like a jewel. Underworld Dreams also really hurts them, and each opponent equally well for multiplayer..

Cheers

Dark Depths is certainly a land to consider. It allows you to win if your opponent choose to slow down the game.

it's basically a death clock that force them to play fast and hence loose life through your stuff. And it's on a land so it can't be countered.

I know its a little outdated but have you considered splashing red for Citadel of Pain?

Omg Citadel of Pain is an absolute beast of a card.