If Ride the Shoopuf becomes a creature but you haven't controlled it continuously since your most recent turn began, you won't be able to attack with it that turn
Agent of the Iron Throne provides retribution for destroy effects for your artifacts or creatures, and if you can set up a recursion loop for a creature or artifact, Agent of the Iron Throne can be your win condition
Eleven, the Mage is a Grixis 3/5 Human Wizard, costing one generic, one blue, one black, and one red
Exiling additional copies does nothing in Commander, making these overcosted Stone Rains for little benefit
Lastly, note that "mana cost" was originally called "casting cost" up until the release of the Sixth Edition core set, which brought a number of important rules and terminology changes
Its like Slay the Spire for adaptive deckcraft, but filters it through escape-room puzzles and fourth-wall tricks that keep every run unsettling