Particle systems can have a subparticle attached

game/engines/default/engine/Particles.lua

game/modules/tome/data/gfx/particles/bolt_fire.lua

game/modules/tome/data/gfx/particles/fireflash.lua

game/modules/tome/data/gfx/particles/firetrail.lua

game/modules/tome/data/gfx/particles/flame.lua

game/modules/tome/data/gfx/particles/gravity_well.lua

game/modules/tome/data/gfx/particles/gravity_well2.lua

...modules/tome/data/gfx/particles_images/distort_shield.png

game/modules/tome/data/gfx/shaders/distort.frag

game/modules/tome/data/gfx/shaders/distort.lua

game/modules/tome/data/gfx/shaders/fireball.frag

game/modules/tome/data/gfx/shaders/fireball.lua

game/modules/tome/data/gfx/shaders/plasma.frag

game/modules/tome/data/gfx/shaders/textoutline.frag

game/modules/tome/data/gfx/shaders/textoutline.lua

game/modules/tome/data/talents/chronomancy/gravity.lua

src/particles.c

src/particles.h