There's sonichu, pikasonic, and this bootleg pikachu/sonic game created in 2000A user responding to one of CWC's tweets has shared this screencap:
View attachment 497785
Here is an archive of the original Tumblr post:
If this is true then Pikasonic may very well predate Sonichu. There are 0 mentions of Pikasonic on KF so I thought it worthy to post even if its complete bullshit.