REDU format ruling
Colosseum - Cage of the Gladiator Beasts

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Place 1 Counter on this card each time a monster is Special Summoned from either player's Deck. All "Gladiator Beast" monsters gain 100 ATK and DEF for each of these counters on this card. If this card would be destroyed by a card effect, you can discard 1 "Colosseum - Cage of the Gladiator Beasts" to prevent this card from being destroyed.
Rulings
- The effect that places 1 Counter onto "Colosseum – Cage of the Gladiator Beasts" whenever a monster is Special Summoned from a player’s Deck begins a Chain.
- Discarding 1 card to prevent "Colosseum – Cage of the Gladiator Beasts" from being destroyed by a card effect does not use the Chain. You discard the 1 card when resolving the effect that should destroy "Colosseum – Cage of the Gladiator Beasts".
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.