You may cast one only during your own main phase when the stack is empty
You can discard just one card or two, and that depends if you want raw card advantage or more cards in your graveyard
Exit Through the Grift Shop Felidar Sovereign Form of the Approach of the Second Sun Frenetic Sliver Gallifrey Stands Gideon of the Trials Halo Fountain Happily Ever After Hedron Alignment Helix Pinnacle Hellkite Tyrant Herald of Eternal Dawn Jace, Wielder of Mysteries Laboratory Maniac Laboratory Maniac Liliana's Contract Luck Bobblehead Mayael's Aria Maze's End Mechanized Production Mortal Combat Near-Death Experience Now I Know My ABC's Platinum Angel Platinum Angel Avatar Ramses, Assassin Lord Revel in Riches Shahrazad Shinryu, Transcendent Rival Simic Ascendancy Test of Endurance Thassa's Oracle The Book of Exalted Deeds The Cheese Stands Alone The Countdown Is at One Triskaidekaphile Twenty-Toed Toad Woodland Guidance Wowzer, the Aspirational (playtest)
As with their predecessors, new events are triggered when certain conditions are met, but this time entire creatures like a Shiva summon can evolve and change as a result
The Fair Diamonds Sky Diamond completes the cycle of two-mana rocks that enter tapped, alongside Fire Diamond, Charcoal Diamond, Marble Diamond, and Moss Diamond
