I've just spent AGES checking my Sonic and non-Sonic carts on my Genesis, to see what they do when locked-on to S&K. I also used my cart-switching trick to get the cart ID codes (at the top of the Get Blue Spheres screen), and the codes to access the special stages in Sonic 1 & Knuckles.
| Game | Lock-on effect | Cart ID | Special Stage code |
| Sonic 1 | Special Stage Challenge | 000016643 | |
| Sonic 1 Jap | Special Stage Challenge | 000016643 | |
| Sonic 2 | Knuckles in Sonic 2 | 045684907 | 2205 5701 0911 |
| Sonic 3 | Sonic 3 & Knuckles | ||
| Sonic & Knuckles | 014702064 | 2450 9098 7967 | |
| Sonic Spinball | Special Stage | 044795354 | 2548 9729 0199 |
| Sonic 3D Blast | S&K alone | 165949590 | 2252 2613 8304 |
| Sonic Compilation | Special Stage Challenge | 000016643 | |
| Skitchin | Special Stage | 064252743 | 0719 2353 3984 |
| Ristar | Special Stage | 059340366 | 2690 6073 3932 |
| Mega Bomberman | Special Stage | 045869299 | 0401 6450 8463 |
| Micro Machines 2 TT | Special Stage | 175432328 | 2501 9641 9872 |
| Rocket Knight Adventures | Special Stage | 149626613 | 1892 6465 0606 |
| Sparkster | Special Stage | 149364151 | 2236 1364 8422 |
| Bubsy the Bobcat | Special Stage | 163848525 | 0064 3557 6936 |
| Bubsy the Bobcat 2 | Special Stage | 163800848 | 2340 2318 5760 |
| World of Illusion | Special Stage | 044936077 | 1174 8779 6191 |
| Zool | Special Stage | 047292245 | 0144 5760 1003 |
| Mortal Kombat | Special Stage | 264317766 | 2458 7633 3867 |
| Mortal Kombat 2 | S&K alone | 240525102 | 0206 0941 2515 |
| Mortal Kombat 3 | S&K alone | 031023194 | 2512 1263 9287 |
| James Pond 2: Robocod | Special Stage | 039168532 | 1129 9312 8219 |
| The Aquatic Games | Special Stage | 038033190 | 1731 2907 8163 |
| The Lion King | S&K alone | 139490076 | 0217 2548 7282 |
| Lemmings | Special Stage | 049966780 | 1731 5683 5487 |
| Toejam & Earl 2 | Special Stage | 061094908 | 2393 7344 5012 |
| Altered Beast | Special Stage | 136845043 | 1247 4851 1304 |
| Virtua Racing | S&K alone | 016081867 | 2450 8259 9399 |
| Beavis & Butt-head | Special Stage | 265467201 | 0869 2711 0637 |
| Cool Spot | Special Stage | 150165183 | 0432 4039 7780 |
| Puggsy | Special Stage | 216696449 | 0196 6148 1323 |
| Street Fighter 2 SCE | S&K alone | 006988767 | 2705 9340 4903 |
| Street Racer | Special Stage | 149118679 | 1377 0806 0346 |
Notes:
Special Stage - NO WAY screen with dark, non-animated characters
+ single Special Stage
Special Stage Challenge - NO WAY screen with light, animated
characters + Special Stage challenge with over 65535 levels.
S&K alone - Sonic & Knuckles game, as if no cartridge was
locked-on.
Games that have no cart ID or code don't work with S&K in
this way.