Oh, and if you think
Burn Everything is interesting, look at
Surging Flame:
This his hilarious as a pyromancer. With a little trivial set-up (hit an enemy with a fire power),it turns any fire resistance into Vulnerable 5 fire. In combo with Burn Everything, even immune creatures take extra damage.
"Doot dee doo, I am a fire elemental, I bathe in lava."
"G'day, mate, I'm a fire mage."
"LOL, I can bathe in your fiery doom."
"Well let me wash you. Pew pew pew!"
"OW! THIS HURTS MORE THAN ANYTHING. YOU ARE BURNING MY LACK OF FLAMMABILITY. I AM MADE OF FIRE AND NOW I AM MORE ON FIRE THAN BEFORE. THIS MAKES NO SENSE."
Sympathy of Flame is not awful in combination with any weapon property that deals ongoing fire damage (flameburst, infectious flame, flaming), though getting that sweet incendiary dagger superior implement is a hefty feat fine for a mage (they don't have proficiency with daggers as an implement). Stoking the Fire isn't great, but it stacks, so it's overkill.
That's all before you leave heroic.
BOOM BOOM BOOM