The "0525" build of Sonic & Knuckles is a prototype build of Sonic & Knuckles for the Sega Mega Drive. It claims to have been built on May 25, 1994 at 15:28.
This prototype was released by drx during the February 23rd, 2008 proto release. This prototype differs from the other Sonic & Knuckles prototypes in that it is already locked-on to Sonic 3 (final version). By itself, this prototype will not boot. A savestate (info) (21 kB) has been produced that allows the game to be played alone, but it is very "broken"; the level art doesn't load correctly, any type of boss (including Knuckles at Hidden Palace) will crash the game, Badniks do not appear (but still function correctly), and the list goes on.