My only issue with Containment Priest is that it's yet another creature that makes me want to keep my Vial on 2. The deck works better the less I have to second-guess play decisions.
If Containment Priest were modern legal, i dont know why anyone would even play it in Death and Taxes. It ruins your own gameplan.
You are probably right about the lands, dropping a Painful Truths is easily done. I kind of like the idea of Mentor here because all we will be casting pretty much is Noncreature spells which will trigger him and gum up the board and Wall of Omen could be good yes, but it doesn't really do much other then draw a card go, if i'd run walls i'd want 4, not 2.
This list is really rough and something I just threw together at the spot so not tested yet. I was thinking Ayli, Eternal Pilgrim could be cute here for when you cheat Emrakul in, if you can't flicker it, you can sac it and reshuffle your graveyard back in and gain 15 life, she's also a solid blocker and easier on the curve.
I'll see if I can spare some time to test the list tomorrow.
Could 23 lands be enough or would it really require 24?
You can't target Emrakul with Resto, since it has protection from colored spells. Ayli doesn't target, so that synergy would work, but I don't know if it is worth it. If you've played an Emrakul, you've already won at that point.
At less that 24 lands, you'll have a less than 60% chance of playing Nahiri by turn 4. If you look at any of the major lists floating around with her, they run 25 lands since the deck hinges on playing her on time. I don't think there is any problem with running 2 walls, at least then you have some good flicker targets.
"You can't target Emrakul with Resto" This isn't actually true, when Restoration Angels bounce is put on the stack, Restoration Angel is a Permanent, and no longer a spell. Thus it can target Emrakul.
Displacer would go to your hand
If Containment Priest were modern legal, i dont know why anyone would even play it in Death and Taxes. It ruins your own gameplan.
"You can't target Emrakul with Resto" This isn't actually true, when Restoration Angels bounce is put on the stack, Restoration Angel is a Permanent, and no longer a spell. Thus it can target Emrakul.