Arduino-based voice changer with LED matrix animated face.
This is a heavily modified/mutated/optimized version of the adavoice_face sketch from the Adafruit Wave Shield voice changer project:
http://learn.adafruit.com/wave-shield-voice-changer
Specifically, this exact version is used in 'Spark the Demon':
http://learn.adafruit.com/electronic-demon-costume
This code is provided here for the curious (and people running up against RAM and flash imitations in their own e-demon derivative projects), but please be aware that it does some really uncouth things, might not be compatible with your hardware and probably contains nasty bugs. This is further explained in the code.
Free, but no support, use at your own risk.