We cant quite determine what theyre doing, but they seem to be doing it quite well. Vedalken research notes Watermark: Mirran Illustrated by Greg Staples Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Legal Brawl Not Legal Legacy Legal Comp
That means you decrease the probability of drawing them later
When a fused split spell resolves, follow the instructions of the left half first, then the instructions on the right half
While other players can stop you drawing from Esper Sentinel, more often than not, they won't want to wait an extra turn to play their spells, more or less ensuring the card at least replaces itself
Youd much rather have Krothuss in your command zone without jumping through all the hoops, but youve gotta go through Runo first
Dragon decks, Treasure-themed decks, and any red deck in need of ramp could benefit from running Goldspan Dragon