source 1: tcrf.net page about sonic 2.
source 2: hidden palace nick arcade prototype.
source 3: hidden palace simon wai prototype.
source 4: hidden palace aug 21 1992 prototype.
source 5: hidden palace sep 14 1992 prototype.
source 6: hidden palace aug 21 1992 prototype.
source 7: hidden palace beta 4 prototype.
source 8: hidden palace beta 5 prototype.
source 9: hidden palace beta 6-B prototype.
source 10: hidden palace beta 6 prototype.
source 11: hidden palace beta 7 prototype.
source 12: hidden palace beta 8 prototype.
