As the original S3K rom is 4MB, jEnesisDS has the limit of running <3MB roms. To get it to work on jEnesisDS, use this patch. (Mirror, including a patch to fix SRAM.) Use WinIPS: http://fuji.drillspirits.net/winips/ to patch it to the clean Sonic & Knuckles (NOT Sonic 3 & Knuckles) rom. This patch puts all the Sonic 3 stuff excluding the Competition/2 Player stuff in the rom. As the Competition/2 Player stuff are excluded, selecting Competition in the title screen will take you to the Blue Spheres Game ("NO WAY! NO WAY! NO WAY?" press A+B+C). The SRAM doesn't work, so you have to use Save States. This is a jEnesisDS problem. Enjoy playing Sonic 3 & Knuckles on jEnesisDS!