Delver of Secrets in and of itself isn't particularly broken
It's a *blue* common. It's broken, just not enough to be banned. Even without other things that make it super broken, it's pretty broken. Turn 1, Delver, turn 2, 2 more Delvers, turn 3 swinging for 9 flying damage from mono blue? 4 Delver, 4 Snapcatser and some blue cards you found on the floor beat a lot of Modern decks.
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