Advanced format ruling
Fossil Dyna Pachycephalo
Card effect (current official text)If this card is flipped face-up: Destroy all Special Summoned monsters on the field. Neither player can Special Summon monsters.
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.