REDU format ruling
Poison Fangs

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Each time a Beast-Type monster inflicts Battle Damage to your opponent, inflict 500 damage to your opponent.
Rulings
- You cannot activate Barrel Behind the Door against the damage caused by Poison Fangs, since it is a Continuous Spell Card.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.