Both of these seem to happen at higher, faster levels, beyond level 4 or 5.³
Sound cut-out: Get into any spot where you can be safe (not move) for a while. After a few minutes, the "beat" sound will start getting cut out more and more, and eventually the game will go silent! Moving resets this glitch, but it can be done over and over. The technique may work at lower levels, but takes longer.
Dropping pills: Sometimes when K.C. eats a power pill, all remaining pills shift down 1 or 2 pixels. This can happen more than once; sometimes the last pill can go so low that K.C. cannot nab it in a horizontal direction, because it goes below him!
ROM Hacks
PacMan
In 2000, Raindog created a graphics hack of K.C. Munchkin! that makes the game resemble the arcade version of Pac-Man, with changed colors and altered sprites. Raindog never completed the hack because the Odyssey² cannot produce the color yellow. You can download the hack here.
Beast Munchkin
A graphics hack by Ken "Grimlick" Scott that changes K.C. and the Munchers into insectoid characters from the animated series Transformers: Beast Wars You can download the hack here (click on the Odyssey2 link under "My Hacks").