The ".dat_mcr" is related with the file created by Minecraft, an open-ended 3D construction game. The file saves a backup of the level.dat file when the newer version of the game updates from the older "Region" (.MCR) format to the newer "Anvil" (.MCA) format. The level.dat_mcr file can be restored to the level.dat file if you want to revert to the older world format.