MTLib is a library mod for use by Crafttweaker addons, it does not have to be used, but it does provide some helpful methods and classes to make Crafttweaker addons easier to create.
This includes all of Modtweaker util / helper classes, such as the IUndoable action classes and base command "dump" classes.
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If this is a dependency for Minetweaker, then let us know on Minetweaker as well. Just a simple text reference to old versions of MC will work nicely. Thank you and thank you for your amazing mod.
In reply to mixheart:
As far as I know, it's not a requirement, it's a library for addons rather than the main mod