I've been looking into glitch stages in Balloon Fight GB, the Japanese enhanced version of the Game Boy game Balloon Kid. I feel it is a change to something like for example Super Mario levels in which glitch levels have been researched relatively well (which makes me wonder what glitch Kirby's Dream Land, Trip World stages there might be).
Years ago I got at least one of these to work in Balloon Kid as well. I don't know anything about glitch worlds in Hello Kitty World for Famicom (based on Balloon Kid but with Hello Kitty instead) however.
To access a glitch world use 01XX07C0 on the stage select screen and press A.
A glitchy Vs. Stage. Samm appears.
A glitchy Vs. Stage. A glitchy Samm appears.
Another glitchy Vs. Stage with a glitchy Samm.
0D (Stage-| ||):
Balloon Trip mode but you get multiple attempts. You don't get a Game Over screen however, just the 'failed' jingle from the original Balloon Fight and are sent back to the title screen.
0E (Stage-|| ||):
Takes you to the bonus room where you have to get balloons from pipes. Later you are warped to a glitchy exit. The game said Stage 1 cleared and unlocked Stage 2.
0F (Stage 'right side of a blue zero on the left and white space on the right'):
A sound effect for getting knocked out plays. The game loads a glitchy screen and freezes.
I've looked into the Stages up to $50 and there were no more Stages that actually load something and keep it, unless the memory could be adjusted for the Stages which execute RAM. Hopefully there will be more Stages which do and are worth noting.
Perhaps all of the aforementioned Stages are technically used but they were loaded in the wrong way.