I just found out about this tonight. Alex Hirsch sings a few theme songs to Disney Channel and Disney XD shows, some of them horribly:

Andi Mack (the only one he sings right):
https://www.youtube.com/watch?v=oodhQR5uul0

Star vs. The Forces of Evil:
https://www.youtube.com/watch?v=3de8y4vBRjg

Phineas and Ferb:
https://www.youtube.com/watch?v=2fr7uSjJibg