Advanced format ruling
Doomkaiser Dragon/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". When this card is Special Summoned, Special Summon any number of Zombie-Type monsters from either player's Graveyard(s) to your side of the field. Those monsters' effects are negated, and they are destroyed during the End Phase this turn. When this card on the field is destroyed, you can Special Summon 1 "Doomkaiser Dragon" 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.