Blue is everything a combat loving player dislikesways to bounce creatures, ways to avoid damage (especially if Green is involved), and the good old Counterspell
Insight Engine It took a little nudging to remind people this came in their Edge of Eternities precon, but after just a few months people caught on to just how much card advantage you could squeeze out of Insight Engine
6 sweepers, 6 counterspells etc
Even without the latter, Prossh pairs well with cards that benefit from sacrificing creatures, like Blood Artist, or ETB effects like Purphoros, God of the Forge
And sometimes, the decks focus is something silly like Ramirez DePietro being awesome, getting a ship, pirates, stolen booty (artifacts from opponents most often), a cannon, and Ramirez at the helm
I like them less than fastlands but I think theres a real argument that theyre an improvement on the Drowned Catacomb-style duals in many Cubes