Trying to remember the name of it, it's the one in 1.7.10 that caused wither skeletons to spawn like crazy in the nether fortresses, a little bug that I have no idea if it ever got fixed. But it was a neat tool that let me diagnose laggy areas as it would show a list of blocks and tile entities that were causing lag and even highlighted them if you clicked on it in the list so you could figure out what's causing lag and maybe go with another mod's items. Anyone remember what it is and if it's been updated to 1.10.2? Or, heck, it's successor?