This deck revolves around:

Early game:

- Control early menaces with Eliminate, Elspeth's Nightmare and if absolutely necessary Baleful Mastery (by paying the student's cost). You can use Vanishing Verse if you are certain you won't need it later.

- Fix hand with scry lands and Mazemind Tome.

- Destroy opponent's gameplan with Agonizing Remorse and keep in mind you might have the chance to play the card you exile with Ashiok, Nightmare Muse.

- Mana management: As a general rule, once you have a black source on the board, every other lands should be blue or white until you have what it takes to cast Dream Trawler (unless of course you have an abundance of black card in your hand).

- Negate can be used but should absolutely be held if you think your opponent plays disgusting spells like Emergent Ultimatum.

Mid game:

- Deal with Crawling Barrens and Faceless Haven with Eliminate and Baleful Mastery. If you suspect the opponent plays these lands, you will need to deal with them.

- Clean board with Extinction Event. Patience can be extremely rewarding with this spell (especially if you have intel with Agonizing Remorse and Elspeth's Nightmare).

- If you suspect the opponent is heavily playing with his graveyard and if you do not need to immediately deal with a menace, hold on your Elspeth's Nightmare for better value (after all it is food for Ashiok, Nightmare Muse)

- Deal with planeswalkers and big creatures with Baleful Mastery.

- Deal with enchantments if you need to with Vanishing Verse.

- Prepare endgame by playing Cosmos Elixir and Midnight Clock. Your health will be very often low in this phase (it is normal), but you will very often survive thanks to Cosmos Elixir and Mazemind Tome. If your health is high, you will have unmanageable card advantage. You can crank your Midnight Clock, but always bluff that you have a counterspell in your hand (especially if you used Negate before). More importantly, do not crank Midnight Clock too much if you are about to put Dream Trawler on the board. If your are daring, you can play three Cosmos Elixir, but you are playing with fire (especially if you burned most of your Midnight Clock).

-  Note: You can use the health boost from Mazemind Tome before the end of your turn to make sure your Cosmos Elixir draws you a card if you need to burrow your deck for something quickly.

- Deal with big spells with Disdainful Stroke unless, once again, you suspect your opponent if about to play a crazy spell later on.

End game:

- Ashiok, Nightmare Muse will often be your win condition, but most of the time it will be used as bait to let Dream Trawler resolve later. If your opponent can't deal with it, you most likely have awesome spells to steal from his exiled cards so they will do everything they can to deal with it. Even if you know your opponent has something to deal with it in his hand, it is worth playing it anyway for a nightmare token creature and to gain some time by forcing your opponent to burn mana. (If you play against rogue and if you have the chance to steal Ruin Crab three times I highly recommend to do it).

Always keep in mind that when you select spells in your opponent's exiled cards, the first spell is the last one you cast and the last selection will be the first one you cast. (For example, board wipes should be the last selection, especially if other selections are creatures).

- Dream Trawler is your main win condition. Hopefuly, at this point, you should have a very healthy card advantage so everything that targets Dream Trawler can be avoided by discarding cards. What you really want to avoid is Extinction Event (because if your Dream Trawler ends up dying from a wipe, you can always get it back later with Midnight Clock).

There are some things to consider here: for example if you have the mana to crank you Midnight Clock two or three times (as needed), you should attack with your Dream Trawler first, if your opponent does nothing THEN you crank it up to 12 counters and then you give a sweet +7/+7 to your Dream Trawler because if your opponent targets it with a spell before you attack, you will be forced to tap it and it will waste the buff.