Forge 1.13+ uses the Forge team's CoreMods project instead of the Sponge team's Mixin project.
Forge 1.12 uses the Sponge team's Mixin project, which does not require MixinBootstrap.
If you experience any crashes with 1.12, you may need MixinCompat or to rename MixinBootstrap as detailed here.
Other Mods:
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