REDU format ruling
Obsidian Dragon

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Negate the effects of Spell and Trap Cards that target only 1 face-up DARK monster you control, and destroy them.
Rulings
- Obsidian Dragon's effect is a Continuous Effect.
- Equip Spell Cards equipped during a previous turn will be negated and destroyed by Obsidian Dragon's effect.
- When a Union Monster is equipped to a DARK monster you control, it is negated and destroyed by Obsidian Dragon's effect after equipping to the DARK monster.
- If you use Snatch Steal to take control of your opponent's DARK monster while you control Obsidian Dragon, Snatch Steal is negated and destroyed, and the DARK monster is returned to your opponent.
- If you use Brain Control to take control of your opponent's DARK monster while you control Obsidian Dragon, the effect of Brain Control is not negated.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.