John's World
Level 2 Room 5 features a Town of ZZT-style combination lock where you must push columns of sliders and boulders by amounts corresponding to the correct digits of the code, and then push the switch to check if the input is correct. Incorrect input forces you to reload the game, while correct input causes a pusher to push a row of sliders until it unlocks a one-way gate to the next room.
However, there are two rows of open space too many north of the locking mechanism, and there is nothing east of the last digit of the mechanism other than a single east-west slider. As a result, not only is there enough room to push the column for the last digit all the way up and out of the mechanism, but the player is then able to run up to the gate, push it east once, and then circle around to push its boulder out of the way to exit the room, as if the correct code had been entered. This also allows you to backtrack, unlike opening the gate as intended.
In the Level 1 key room, it is possible to find a hidden treasure that is intended to give you lots of health, ammo, gems and points when collected, but silently fails to do because its #give commands state the counters and the amounts to add to them in the wrong order (they state the amount first instead of the counter). No other #give commands in the game are written this way.
The Level 3 Key Room, accessed by going west from the Level 3 hub, does not have a board exit back to the Level 3 hub, and thus the game will become unwinnable as soon as you enter it. The only way to complete the game without cheating is to use the red key acquired in Level 3 Room 4 to open the red door in the overworld rather than the red door in the Level 3 hub that you're supposed to open with it.
