Tortured Spark

Enrage — Whenever Tortured Spark is dealt
damage, put a rage counter on it. Then if
Tortured Spark has three or more rage
counters on it, exile it, it deals 10 damage
to each creature and each player.

It is unknown why the ignition of a pyromancer's planeswalker spark in particular causes such an effect. Frankly, most are unwilling to investigate.