Tengu format ruling
Rapid-Fire Magician

Card effect (current official text)Inflict 400 damage to your opponent each time you activate a Normal Spell Card.
Rulings
- This card’s effect is a Continuous Effect that cannot be chained to.
- The 400 points of damage is inflicted after the effect of the Normal Spell Card is resolved. So if the opponent had 300 Life Points, and you activated "Rain of Mercy" while you had "Rapid-Fire Magician" face-up on the field, the opponent would gain 1000 Life Points, and then take the 400 points of damage, leaving them at 900 Life Points.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Tengu forum — sourced change requests get reviewed.