Deck I'm slowly building. The theory:

Justifications on cards:

The mana base:

Instead of running utility lands and more fetches, or a more aggressive shockland mana base, I've opted for three man-lands to help provide finishers for the deck, but also five basics. The basic lands are partially because I expect to run into Blood Moon a lot (and 12 ways to access basics sounds like a must), but also because I expect to see a lot of Path to Exile and Ghost Quarters.

The Darkslick Shores is simultaneously the best and also the worst land in the deck. It allows turn 1 Delver and easy access to Thoughtseize... but it comes in tapped as our ideal untapped turn 4 source for Mentor + spells. There is a strong argument for running 4x Watery Grave instead of them, but it's my thought that between Watery Grave, Thoughtseize and Anguished Unmaking that our aggressive match-ups would suffer without making more room for removal and sweepers in the board. This means intelligent sequencing of lands is needed to minimize the chance of a turn 4 Shores. When it comes down as land numbers 5-6, we care less than land number 4.

The cantrips:

Between the three cards we run 12 cantrips, making the rest of the deck slightly slower and more consistent.

The removal:

We run Path to Exile as the best general-purpose spell. Anguished Unmaking is a catch-all card that ought to help us deal with other problem permanents (notably Planeswalkers and Artifacts) to help swing match-ups like Affinity and Jund/Abzan more in our direction. A singleton Slaughter Pact is run to help synergise with Mentor, but more are not run because drawing them in multiples is often painful and it limits the amount of cards we need to sideboard out in certain match-ups (e.g. when Tasigur/Angler/Bob/Kalitas are the creatures to beat).

Other:

We run a singleton Emerge Unscathed. It protects our creatures, can make our Tasigur unblockable, act as a combat trick, or double-triggers Mentor. It's also terrible on an empty board, making it a fun-of, rather than a game plan. It doesn't synergise as well with Snapcaster Mage as I would like, but is still decent if milled, making it fairly powerful when not drawn in multiples.