Advanced format ruling
Black Horn of Heaven
Card effect (current official text)When your opponent would Special Summon exactly 1 monster: Negate the Special Summon, and if you do, destroy it.
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.