REDU format ruling
Triggered Summon

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Activate only when a monster is Special Summoned to your opponent's side of the field. Each player can Special Summon 1 Level 4 or lower monster from their hand.
Rulings
- You can choose not to Summon a monster when this card resolves.
- You can activate this card if you have no Level 4 or lower monster in your hand.
- You cannot activate this card if neither player has an open Monster Card Zone. You can activate this card if only 1 player has an open Monster Card Zone.
- When this card resolves, the Turn Player Summons first, but both players’ monsters are considered to have been Summoned at the same time.
- You can activate this card when you Special Summon Lava Golem to your opponent's side of the field.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.