REDU format ruling
Yubel

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)This card cannot be destroyed by battle. You take no Battle Damage from battles involving this card. Before damage calculation, when this face-up Attack Position card is attacked by an opponent's monster: Inflict damage to your opponent equal to that monster's ATK. During your End Phase: Tribute 1 other monster or destroy this card. When this card is destroyed, except by its own effect: Its owner can Special Summon 1 "Yubel - Terror Incarnate" from their hand, Deck, or Graveyard.
Rulings
- Yubel's damage inflicting effect is a Trigger Effect that activates before damage calculation.
- Tributing 1 monster or destroying Yubel is a Trigger Effect that activates during your End Phase. You make your choice when the effect resolves.
- When Yubel is destroyed while in the hand or Deck, its effect activates. If it is destroyed while face-down, its effect activates.
- The owner of Yubel activates the effect. (If your opponent controls your Yubel when it is destroyed, you get the effect, not your opponent.)
- When Yubel is destroyed during the Damage Step, its effect can be activated.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.