Advanced format ruling
Gemini Booster
Card effect (current official text)Equip this card to a Gemini monster you control as an Equip Card. It gains 700 ATK. When this card is destroyed while equipped and sent to the Graveyard, select 1 face-up Gemini monster and treat it as an Effect Monster.
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.