Campfire
This is just me trying to simulate fire in Pico8 without shaders or fancy particle systems.
My approach is :

At load time :

Generate bursts of animated particles
Each particle increments the brightness value for the pixels it sits on
The burst animations are baked into the spritesheet

At run time :

Animate the baked sprites (moving them up)
Again, add the brightness values together

The brightness value (which is just a color from 0 to 7) is mapped to a fire shade with pal().
There are other particle systems for bursts of sparkles and fireflies.
Any thought? What would be your approach?
v2 update

use colors 0 to 7 for fire shades : no table needed to store brightness values
bake animations into spritesheet for performance
got rid of smoke
add flickering
nicer fireflies and flying ember
add clouds

v3 update

press a button to toggle scene onoff (monitor CPU usage of fire only)