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Setting the value of the RAM address $338 to 02 (or using the Game Genie code ZAOEAPAA) at the Rocket Jockey game menu will bring the player to Level 3. This is a semi-playable level with a wrongly colored background, and sprites that glitch out when certain enemies appear. There are also mountains in the background that don't appear elsewhere in the game, as well as projectiles that spawn periodically.
Contributed by Gamer#1
There is evidence is the game's code that suggests that there was originally going to be 8 more games, making a total of 60.
Contributed by xianc78
In Cheetahmen, each character has its own introductory cutscene. However, the cutscene for Apollo appears to have no text accompanied with the obligatory image. This is because Active forgot to put the alphabet characters next to the image tiles in the ROM. The unused text can be found in a memory viewer during the cutscene and Levels 5 and 6 of Cheetahmen, and reads:

"APOLLO IS THE MASTER OF THE CROSSBOW. USE THE CROSSBOW TO DEFEAT THE ENEMIES ON THE LAST TWO LEVELS AND GET DR. MORBIS"
Contributed by ShyanVixen
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A contest was planned in which anyone who completed level 5 of the game "Ooze" would be entered in a drawing for $104,000. However, the game locks up on level 2, making this contest impossible. The message can be seen through the use of hacking tools.
Contributed by DeerBoarDude