Super Adventure Box

Love or hate the Box but it delivered some fairly unique mechanics into the game (e.g. no fall damage), mechanics that people can play around with to get to awesome places:

 Glitch City

This reminded me of Sunshine City from Pokemon Red/Green, which you could reach by glitching the safari zone. Sadly the way to get there was patched out of the game as it involved the geysers going up and down. Although the video footage I have is a little old it still shows off stuff we havent seen in the SAB yet. For example underwater visuals.

Timestamps:
2:33 Rainbow
4:03 Map Cinema
17:20 Rapids level
18:15 Super Underwater visuals and mechanics (no mechanics...) in bonus stage??
29:36 Huge Slingshot (Log template?) and lots of other random template stuff in the following minutes.
34:55 King Toad