Eidolon of the Great Revel
Enchantment Creature — Spirit
Whenever a player casts a spell with mana value 3 or less, this creature deals 2 damage to that player.
Xenagos reveled while Theros burned.
2/2
Illustrated by
The List#JOU-94RareEnglishLegality
Rulings
Mar 16, 2018
Casting Eidolon of the Great Revel doesn’t cause its own ability to trigger. It must be on the battlefield when the spell is cast for its ability to trigger.
Mar 16, 2018
The amount of mana spent to cast a spell doesn’t change its converted mana cost. For example, a card cast with its morph ability has a converted mana cost of 0 even though 
was paid.
Mar 16, 2018
The converted mana cost of a spell with 
in its mana cost includes the value chosen for X.