This article's content is accurate to the most recent public game version, 0.4.8d.
"Natalie's magic deals fire damage to one enemy. A bit more violent than you were expecting."
Cost: 4 MP
Source: Natalie - Starting skill.
Brimstone Blast is a spell that deals moderate 
Fire damage to a single enemy.
Early on, this is Natalie's primary means of dealing significant damage to opponents. Even later in the game, this remains a viable and cheap spell to use.
The following enemies can cast Brimstone Blast: