More R&D for the current project. The Hue Fizzler takes a rainbow ID pass and slices it into discrete color bands using hue quantization - pick how many segments you want, and you've got that many independent ranges to target in your ID pass.
Noise runs through each segment, and segments can be killed off independently, which lets the mask break apart in a flickery manner instead of fading uniformly.
In other words, it makes your mask fizzle out in interesting ways. Useful for sparks, plasma explosions, etc etc.