Mono-Blue Faeries is full of small flying creatures like Spellstutter Sprite, Faerie Seer, and Faerie Miscreant, along with Counterspell to protect its board and disrupt our auras. Thraben Charm's damage equal to twice our creature count is well positioned to kill one of their many 1-toughness Faeries once we have board presence, and it can also destroy an enchantment like Moon-Circuit Hacker, but more usefully it can hit their evasive threats before they chip us down with Ninja of the Deep Hours card advantage. We trim the slower escape-based Sentinel's Eyes since their Counterspell and Spellstutter Sprite make it inefficient to rebuild piece by piece.