Historically, it’s really hard to keep Delver decks down. When mono-blue Delver rose to prominence, it did so in no small part thanks to the interaction of Cloud of Faeries and Spellstutter Sprite. Then came the era of Augur of Bolas and Gush; once Delver decks were at the top of the metagame. Today it is Mystic Sanctuary and Tragic Lesson that is helping to propel Delver style decks to the top of Pauper. But this time, honestly, I believe it is different.
Let’s start on Saturday, May 23rd. Half of the Top 8 were Izzet Mystic Sanctuary decks and this pattern was repeated in the Top 16. These decks might not be identical but they have a few common elements: Augur of Bolas, Ninja of the Deep Hours, and Spellstutter Sprite as creatures; Lightning Bolt, Skred, and the Mystic Sanctuary package in the spell slot. Whether they run Delver of Secrets or Faerie Seer or neither, these decks have made a solid run at the throne.

How good were Izzet decks on Saturday? Out of 23 possible Win+ points they took home 13 – almost 57%. These are the sort of numbers, if sustained, could be a cause for alarm. Yet I’m not worried at this time. Let’s look at Sunday.

Did Izzet Faeries win the event? Yes. But it was the only Izzet Mystic Sanctuary deck in the Top 8 and one of two in the Top 32. There were only 5 Mystic Sanctuary decks in the entire Top 32. As a reminder, there were 4 such decks in the Top 8 on Saturday.
What happened?
First off, there was a surge in Boros Monarch and Boros Bully. Both of these decks have a traditionally good matchup against Delver-style decks. Second, Affinity came out in force. There are two good ways to fight Spellstutter Sprite and crew. The first is to completely ignore red and blue spells to dodge Hydroblast/Pyroblast. The second is to have access to Hydroblast/Pyroblast yourself. Affinity falls into the latter camp. Affinity is also quite capable of presenting enough large threats to put a premium on Skred use all while setting up a combo kill.
So back to why I’m not concerned at this point in time. When looking at Cloud of Faeries and Gush, these cards presented problematic game states in the very early stages of a game. Cloud of Faeries and Spellstutter Sprite, backed up with Daze, could lock players out of the first three turns of the game. Gush could do its thing as early as turn four without being much of an impediment. Compare this to the Mystic Sanctuary engines (in fair decks). It takes time for these decks to build up the resources to effectively leverage their engine. That set up gives other decks time to find their own countermeasures.
There is a lot of attention on Pauper these days. The lack of problematic Planeswalkers and Companions means that players are coming to the format looking for something else. If this influx continues I expect to see further developments in the metagame as it continues to churn. With that in mind I would come prepared to fight Boros Monarch and Bully next weekend, while also having a solid plan for Affinity.