Just today, Mo'Creatures Extended () was updated and as part of its update, it reorganized the class file system, and consequently MIA crashes as now the creatures are no longer where they initially were. Here is a snippet of the crash log that I got that illustrates this:
net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Minor Integrations and Additions (mia) Caused by: java.lang.NoClassDefFoundError: drzhark/mocreatures/entity/passive/MoCEntitySnake
The snake is now located at drzhark/mocreatures/entity/hunter/MoCEntitySnake

Of course, fixing this would be a dilemma, as then MIA would lose support for the original Mo' Creatures (which has more total downloads) in favor of this new fork of the mod (which is not very noticed right now, not even at 5k downloads). As a person who likes Mo' Creatures, I favor the new version personally only because it fixes a lot of bugs and improves many of the sounds, textures, and models, among a host of other improvement. But it's not popular so I can see how it's very much a dilemma.

Edit: I fixed this issue by disabling the MIA support for Mo' Creatures in the config. Thankfully, Mo' Creatures adds a lot of (but not all) of the integrations added by MIA in its latest update.

Maybe it could dynamically tell if it's the original Mo' Creatures or Mo' Creatures Extended

As of this commit, Mo‘ Creatures Extended is going to disable the MIA integration because we‘re handling compatibility ourselves: Elite-Modding-Team/MoCreaturesExtended@159e01c

Not very pretty but quickly solves the issue for now.