REDU format ruling
Legendary Fiend

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Once per turn, during your Standby Phase: This card gains 700 ATK.
Rulings
- When Legendary Fiend is removed from the field or flipped face-down, the ATK gain disappears.
- When control of Legendary Fiend shifts to another player, the ATK gain is still applied.
- When Legendary Fiend is equipped with Megamorph, first double or halve its original ATK and then reapply the ATK gain.
- If you Special Summon Legendary Fiend during your Standby Phase, its effect activates during that same Standby Phase.
- If Legendary Fiend is equipped with your opponent's Blast Sphere, you can choose to activate Legendary Fiend's effect or pass to your opponent. If they decide to pass, you must activate Legendary Fiend's effect.
- While Skill Drain is active, the ATK gain disappears. When Skill Drain is negated or removed from the field, the ATK gain is not reapplied.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.