Aquatic Ruin zone:
https://www.youtube.com/watch?v=dr3NIDWvbR8&feature=related
Sonic 1 boss:
https://www.youtube.com/watch?v=oNSsLA_ye7Y&feature=related
Sonic 2 boss:
https://www.youtube.com/watch?v=QJumqm9_jz4&feature=related
Sonic 2 final boss:
https://www.youtube.com/watch?v=D7gvSd2kxi4&feature=channel