extends global entity ids to an unsigned byte(0-255) or short depending upon the version you get. that's it that all it does. this mod was created in 1.5.2 for the chocolate craft modpack under 307017709 project. this will allow modpacks to have twice the global entity ids(entity ids with vanilla api also allowing eggs). forge's api uses int but vanilla which alot of mods used still was 127.
mcp > edit instance > versions > add to minecraft.jar > select this mod