EDH Grand Arbiter

Nice, I'm liking the way this is looking. Could be a real pain in the ass to play against. :P
Critiques that I have to offer would include.
1. Dropping Tundra Wolves.
2. Thinning out the mana sources. 38 land is perhaps a tad high when over half of your cards are three mana or less. A lot of the land is utility based, I get that, but you might end up pulling a lot more small utility than game changing lock-down cards, (though I would recommend looking into things like Maze of Ith or Mystifying Maze for added control).
3. Akki Underminer can't be in the deck -doesn't fit the Sen Triplets color scheme.
4. A minor note, Weathered Wayfarer is basically Land Tax that is easier to kill, doesn't function as hard and costs mana to continually use. I would consider the upgrade.
5. If you have white and blue at your disposal, consider things like Propaganda and/or Ghostly Prison. You only have 14 potential blockers, so this may come in handy -so would Ensnaring Bridge now that I think about it, though that depends on if you plan to win by attacking or if you have a combo tucked away.
6. Because you have so many low cost spells, consider adding an Isochron Scepter. There's nothing that says DICK like throwing down an Isochron Scepter with a Boomerang on it turn two and locking your opponent down to only being able to play 2 land the entire game. Also works well with counterspells, tutors and removal.
There are a couple other tweaks I might suggest, but we can talk about it at work.

The thing about Tundra Wolves in an EDH deck in multiplayer; is that it is never seen as a threat; some one else is guaranteed to have a bigger stompy. I want to have a few creatures out that are no threat, to use as blockers. If some one knows how big of a threat this deck is they will all gang up to kill you fast. But by the time they realize what this deck does, it is hard for them to deal with, you are controlling the hand of the biggest threat, countering all big stompies and main combo cards, taking their stompies from the grave or in play to make them your own.

That is also the need for more land; you need to be able to counter at least 2 players a turn and still play a "thief", enchant, artifact or creature card too. So lots of low mana cards and extra mana.

Nice catch on the Akki Underminer.

I like your other card suggestions.