You can find these Buy-a-box promos at certain local game stores
Jenson Carthalion, Druid Exile Jenson Carthalion, Druid Exile rewards you for casting multicolored spells by letting you scry 1, and if that spell is all colors, you get a free 4/4 Angel with flying and vigilance
Hence, you can build a deck that focuses on filling your graveyard with cards that you can later exile to create zombie tokens or use cards that allow you to repeatedly return cards from your graveyard to your hand or library to create a constant stream of tokens
(2025-09-19) If you cast a spell for another cost "rather than pay its mana cost," you can't choose to cast it for any alternative costs
Prismatic had the right idea where it banned fast mana like Mana Crypt and Sol Ring, tutors (ranging from Mystical Teachings to Demonic Tutor), and then any other degenerate cards like Memory Jar, Necropotence, Yawgmoth's Will, or Gush