This project turns a boring lullaby playing toy into a veritable party machine. Videos and pictures can be found on hackaday.io
It uses an ESP8266, drives the speaker via a transistor and 8 WS2812 LEDs
The software is written in Arduino and uses the ESP8266 Audio library.
A custom board using an ESP8266 12E, the schematics can be found here
At boot, the teddy will fetch /playlist which should return a single integer describing how many songs can be fetched. Then it starts playing /songs/0.mp3, if you push the button (that is mounted on the Teddys belly) it will loop to /songs/1.mp3 etc. until it reaches the count described in playlist.