Scourge of Valkas
Creature — Dragon
Flying
Whenever this creature or another Dragon you control enters, it deals X damage to any target, where X is the number of Dragons you control.
: This creature gets +1/+0 until end of turn.
Lucas Graciano
Pioneer Masters (PIO)
• #155Rulings
The amount of damage dealt by the Dragon that entered the battlefield is based on the number of Dragons you control when the ability resolves.
(wotc • 2017-11-17)
If a Dragon entering the battlefield causes Scourge of Valkas's ability to trigger but leaves the battlefield before that ability resolves, that Dragon still deals damage.
(wotc • 2017-11-17)
Rulings
The amount of damage dealt by the Dragon that entered the battlefield is based on the number of Dragons you control when the ability resolves.
(wotc • 2017-11-17)
If a Dragon entering the battlefield causes Scourge of Valkas's ability to trigger but leaves the battlefield before that ability resolves, that Dragon still deals damage.
(wotc • 2017-11-17)