Brash Taunter Burn from Within Crackling Emergence Diamond Pick-Axe Hazoret the Fervent Hazoret, Godseeker Hour of Devastation Myojin of Infinite Rage Myojin of Roaring Blades Old Hob, Alleycat Blues Purphoros, Bronze-Blooded Purphoros, God of the Forge Purphoros, God of the Forge Rebel Salvo Sarkhan, the Dragonspeaker Slobad, Goblin Tinkerer Smite the Deathless Solphim, Mayhem Dominus Soul Sear Ulrich's Kindred
It's far worse than Time Spiral, because Spiral you can use the mana you get back however you want instead of being limited to casting one card, and also you can further abuse the untapped lands with mana doublers like High Tide
Limited availability and intense international demand continue supporting high market values
Cards that remove abilities, like Humility, remove these keyword abilities from your cards