REDU format ruling
Gundari

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)This card cannot be Special Summoned. This card returns to its owner's hand during the End Phase of the turn it is Normal Summoned or flipped face-up. If this card battles a Synchro Monster, return both monsters to their owners' hands at the start of the Damage Step (without damage calculation).
Rulings
- The effect to return "Gundari" and the Synchro Monster activates at the start of the Damage Step.
- If "Gundari" battles a Synchro Monster while "G.B. Hunter" is on the field, "Gundari" is returned to the hand and the Synchro Monster stays on the field.
- If "Ally of Justice Catastor" battles "Gundari" both of their effects activate and form a Chain. If "Ally of Justice Catastor" attacks "Gundari," both monsters are returned to the hand or Extra Deck. If "Gundari" attacks "Ally of Justice Catastor," then "Gundari" is destroyed and "Ally of Justice Catastor" returns to the Extra Deck.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.