(8/7/2020) If you cast a spell "without paying its mana cost," you can't choose to cast it for any alternative costs
1 Undercity Upheaval
Happily, the game's designers didnt stop there
It could be a restriction on card names, artists, art elements, flavour, or any other number of things, but the point is that the deck is built around that quirk
Because there's a pretty firm "ceiling" to how powerful removal can get, Wildcards spent this way will let you play with them for a long time
Mithril Coat is indestructible, and grants the same effect to the equipped creature, making it practically immune to removal outside of exile effects or bounce spells