Donkey Kong 64/Hideout Helm

In the room before the Blast-o-Matic with the tube and the Tiny barrel, you can enter the tube as Tiny without using Mini Monkey by doing a well-timed Ponytail Twirl into the pipe. Video (#3)
- You can also get in with Diddy by just jumping at the pipe repeatedly, but it can cause the game to freeze. Video (#6)
In the room with the Battle Crown door, there is a computer that's to your right as you face the steering wheel. It's near a klaptrap. By jumping onto the edge of it, you can fall through. You can then walk out of bounds, jump into the room behind the coin door, and get the key. Sometimes, however, the key doesn't count in your inventory. It is believed that by walking through the area that contains the coin door, you "activate" the key so that it counts in your inventory if you pick it up. Walking under the coin door seems to achieve the same effect. Video (#13)
If you jump/roll with Chunky toward the top edge of the rightmost computer on the right wall after crossing the lava pit, you can pull yourself through the wall and out of bounds. From here you can walk around Tiny and DK's Blast-o-Matic mini-game sections and jump back in bounds behind the K. Rool door. Video (#2)