Sonic Jam (Game.com)
This game has a prerelease article
The Game.com Sonic Jam is not actually a port of the Saturn version. Rather, it's just a collection of levels inspired by Sonic 2, Sonic 3, and Sonic & Knuckles mixed with bleepy music, ugly black-and-white graphics, inexcusable bugs, and an abysmal framerate.
Press A, A, A, D, D while the game is paused and you'll be granted an extra life.
Press A, B, C, A while the game is paused and you'll be given invincibility.
Early versions of sprites for Knuckles are used instead of the final ones.
Graphics for an earlier version of Sonic & Knuckles, including the larger HUD that can be seen in prerelease material.
"No Lock On"
Presumably, Sonic & Knuckles would have had support for "locking-on" the Sonic 2 and Sonic 3 cartridges for new content, similar to the Saturn version. This would be the icon shown when playing Sonic & Knuckles by itself.
At 0x1072D8 and 0x1078F2 are two unused sounds which depict a female and male moan, respectively. They are leftovers from a fellow Game.com game, Batman & Robin.
The Lost World: Jurassic Park Leftover Text
At 0x525CF is text leftover from the Game.com version of The Lost World: Jurassic Park.
A;B;C;D;E F;G;H;I;J 0;1;2;3;4 5;6;7;8;9 HARDING TEMBO AREA HUMVEE MOTORCYCLE CARGO CARRIER RV;MOBILE;LAB SNAGGER RV;3 STEGOSAURUS PACHYCEPHALOSAURUS TRICERATOPS PROCOMPSOGNATHUS VELOCIRAPTORS TYRANNOSAURUS;REX PTERODACTYLS
In Act 4 of Sonic & Knuckles, a couple of rings which were meant to be placed in a loop are shifted slightly to the right and up of their intended positions.