Planeswalker Challenge - Nightmare Weaver (Casual)

Created for the Planeswalker Challenge - build a deck for any Planeswalker that is thematic, fun to play and accessible.

The simple rules of the challenge:

1. Choose your Planeswalker.
2. Your deck must include 3 copies of that Planeswalker (or, for those that already have theme decks, you can include 1 copy of that Planeswalker and the 2 cards from that deck that tutor that Planeswalker).
3. Your deck cannot include other Mythic cards, and can only include up to 4 Rare and 16 Uncommon.
4. Your deck can only include cards from the same block (or set, post-blocks) as your Planeswalker.

The guidelines for the challenge:

1. Try to create a deck that really shows off what your Planeswalker can do, and that suits their personality.
2. Try to stick to a colour identity that is thematic for your Planeswalker.
3. If your Planeswalker is aligned with a particular faction, try to include only cards from that faction and 'neutral' cards, not cards from other factions.

About this deck:
Ashiok is a tricksy one, and this is a tricksy deck – certainly the most complicated one I've created for this challenge so far. Ashiok's abilities exile cards from your opponent's library, give you the chance to cast any creatures exiled that way, and exile all cards from your opponent's hand and graveyard. Ashiok's first ability could lend itself to a milling deck, but I found with the limitations set by this challenge it was just a bit too slow. Instead I've taken Ashiok's first two abilities together, looking at the potential for snatching my opponent's creatures and seeing what I can do with them. I'm not focussing on Ashiok's -10 ability here – I plan to use Ashiok's -X wherever possible. So, the plan is to snatch my opponent's stuff and beat them with it.
Daring Thief is the key to this plan. Whenever it becomes untapped, you can switch a permanent you control with one your opponent controls that shares a type. This works great with Ashiok's -X, which you can use to cast your opponent's cheap creatures and then switch those for their good creatures! I've also included Vortex Elemental, which works great for you as a blocker, but is practically useless for an opponent with no blue mana – ideal to switch with their best creature.
To get Daring Thief's ability to work, you need to be able to tap it safely. Aqueous Form gives you one way to do this, while Black Oak of Odunos gives you another. Use one of these two cards to enable you to pinch stuff with impunity. At a pinch, you can use Crypsis on an already tapped Daring Thief to steal a creature at instant speed.
As this deck depends on a few key cards, I've made it easier to find them. Divination gives you card draw, but the real star is Disciple of Deceit. This gem of a creature can tutor a card for you each time it untaps, and the same tricks that work for Daring Thief will work for Disciple of Deceit. More than a third of the cards in the deck - 22 cards - are CMC3. This makes it easy to switch the cards in your hand for the the Ashiok, Black Oak or Thief that you need.
Two of the remaining cards are thematic inclusions: Ashiok's Adept for obvious reasons and Thoughtseize as Ashiok is quoted on that card (it's also pretty darn handy). War-Wing Siren is there for a flying blocker – you can make it bigger with Aqueous Form and Crypsis but it's unlikely to win you the game – and Hour of Need is in there to close out the game – spend whatever you can spare to turn your weaker creatures into 4/4 flying Sphinxes and overwhelm your opponent!
Although I did try to include the Ashiok themed cards, Nightmarish End and Tormented Thoughts had to be cut from the deck to enable the key theme of the deck to survive.