Advanced format ruling
Thorn of Malice
Card effect (current official text)Equip only to "Black Rose Dragon" or a Plant-Type monster. It gains 600 ATK. If the equipped monster attacks a Defense Position monster, inflict piercing battle damage to your opponent. If the equipped monster attacks a monster, after damage calculation: The attacked monster loses 600 ATK and DEF. An opponent's monster that battles with the equipped monster cannot be destroyed by that battle.
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.