An X-themed deck lends itself to a lot of neat card choices, since restrictions can be the basis of innovation
Explore means you're potentially dumping all sorts of cards in your graveyard anyway, and Return to the Ranks gives you a handy way to bring these to the battlefield in bulk
A split second spell doesn't clear the stack or automatically resolve it
Subjugate the Hobbits Thats each , my friends
Adding larceny to milling, we get to cast the exiled card spending mana of any type, and we can do so even if Thief of Sanity leaves the battlefield or leaves our control
They often let other merfolk be played from the library, create merfolk tokens when their allies enter the battlefield, or have ways to protect each other that quickly add up