Immibis Core Mod 1.12.2, 1.11.2 includes a set of code and a general API for the mods of Immibis in Minecraft (like Immibis’s Microblocks Mod).
As a supporting mod, Immibis-Core-Mod will not have any effect when installed independently on Minecraft. Instead of that, it will help other mods to run. The mods that Immibis-Core-Mod support will often use a common code structure, thereby to reduce the file size and save time as well as to optimize the system; therefore, the author inserted the code into Immibis-Core-Mod.