REDU format ruling
Alien Brain

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)When a Reptile-Type monster you control is destroyed by battle with an opponent's attacking monster and sent to the Graveyard: Take control of the opponent's monster, and if you do, it becomes Reptile-Type.
Rulings
Activate only when a Reptile-Type monster you control is destroyed by battle with an opponent's attacking monster and sent to the GY. Take control of the attacking monster, and treat it as a Reptile-Type monster.
- This effect does not target.
- The destroyed monster must be Reptile-Type while on the field AND in the GY.
- Use this card in Substep 7 - End of the Damage Step after placing Trigger Effects on the Chain.
- You take control of your opponent’s monster permanently.
- If it is flipped face-down, you keep control but it is no longer treated as a Reptile-Type monster.
- You can take control of Reptile-Type monsters with this card.
- If you control your opponent’s Reptile-Type monster and it is destroyed and sent to their GY you can activate "Alien Brain."
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.