The first level of the game's Story Mode, Siberia, seems to be a reference to GoldenEye 007, the first level of both games are dams in russia, and include similar sounding alarms.
Contributed by Robi Tribal
There is a unused Gothic tileset that can be accessed in gamecube version through the use of action replay. It is listed as "4" in the mapmaker menu.
Contributed by Megamatt867