Advanced format ruling
Venom Swamp
Card effect (current official text)During each player's End Phase: Place 1 Venom Counter on each face-up monster, except "Venom" monsters. Monsters lose 500 ATK for each Venom Counter on them. Destroy a monster if its ATK becomes 0 by this effect.
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.