Advanced format ruling
Red Dragon Archfiend/Assault Mode
Card effect (current official text)This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except with "Assault Mode Activate". If this card attacks, destroy all other monsters after damage calculation. When this card on the field is destroyed, you can Special Summon 1 "Red Dragon Archfiend" from your Graveyard.
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.