High Priest of Penance and Hold the Gates are awesome together, especially if you have more than one of either on the field...

Is the conjurer's closet really necessary? The interaction with Gatecreeper Vine is alright, and switching Mimic targets is okay too, but is it really necessary?

Best rainbow guard deck I've seen so far! +1 (though to be fair I haven't looked around too much for those)

I do believe that Door to Nothingness is irrelevant on Maze End Decks as you would need ten lands / mana.. that's all i can think of at the moment..

The reason I added in Door to Nothingness is due to it only requiring 10 mana, not 10 different gates. With Chromatic Lantern mana-fixing any 10 lands will do.

I've made a somewhat similar deck, and I've found that match-ups against mill decks can be serious trouble. Multiple fallback win conditions greatly helps secure a victory. Lock down your board position so the enemy can't deal damage to you, then win whichever way you want.

Cards you might consider:Sands of Delirium
Jace, Memory Adept
Azor's Elocutors
AEtherling
Assemble the Legion
Garruk, Primal Hunter

I get what all the others are for, but what is AEtherling for?? I don't understand the strategy behind it...

It might not look like it on the surface, but AEtherling is a win condition all by itself. You can pretty easily swing for an unblockable 8 every turn and then exile it during main phase 2. It comes back untapped at the end of your turn, ready to block for you. Additionally, that exile ability makes it extremely difficult to kill, since you can just exile it on top of any stack.

You can even block with it, then exile it before damage is dealt. As long as the opponent's creature doesn't have trample you won't take damage.

In short, AEtherling rocks.

Sweet!!! I didn't see that before! Thanks for the tip. I will definitely be adding AEtherling to my deck!

+1 and why not use Possibility Storm ?