Its a notorious combo piece in cEDH and Modern alike, acting as the linchpin of the bloodpod strategy (often tutoring for cards like Kiki-Jiki, Mirror Breaker)
Arthur's item is the Hard Stone which powers up Rock-type moves
6 Mamoswine ex Everything Is Just In Reach A bit of a situational powerhouse while in play, Mamoswine ex can dish out a lot of damage under the right conditions while giving you a perfect way to set it all up
While it doesnt have a huge competitive history, only seeing occasional Pauper play, this card is somewhat common in Commander
However, as the first Stadium ACE SPEC card to be printed for the game, players can only ever have one of these cards in their decks at a time
Do the ultimate ability of Teferi, Master of Time to win in one fell swoop with this creature in which you have gained control, so you dont have to wait for the full turn cycles to claim victory