Fear of the Unknown [Unknown Event] Jellyfish you may pay {0} rather

you may pay {0} rather than pay the mana cost for a spell you cast with mana value X or less

Set: The List Type: Enchantment Rarity: Rare Cost: {4}{B} Whenever an opponent loses life

Sometimes you just have to go for it

Set: Friday Night Magic 2008 Type: Creature — Human Shaman Rarity: Rare Cost: {1}{G}{G} When Eternal Witness enters the battlefield

Set: Doctor Who Type: Legendary Creature — Time Lord Doctor Rarity: Rare Cost: {4}{G}{U} Time Lord's Prerogative — Whenever you cast a historic spell

Fear of the Unknown [Unknown Event] Jellyfish you may pay {0} ratherSet: Unknown Event Type: Enchantment Creature Nightmare Rarity: Rare Cost: {6} Trample When you cast this spell, choose a playtest card you own from outside the game. Exile it. You may cast that card as long as it remains exiled. Mana of any type can be spent to cast that spell. (In a sealed event, outside the game is your sideboard.)