Advanced format ruling
Marshmallon
Card effect (current official text)Cannot be destroyed by battle. After damage calculation, if this card was attacked, and was face-down at the start of the Damage Step: The attacking player takes 1000 damage.
Current rulings for this card are maintained by Konami.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Advanced forum — sourced change requests get reviewed.