What does the mob attack do? I always assumed it was the the unarmed damage that a mob could do. Like an iron golem being able to punch way harder than a normal player could. It seems like the Iron Golem is the only mob that is able to hit as hard as they normally would, every other mob/morph hits like a normal player. Anyway to fix this? Also, having the default health of a mob already set would be nice, instead of always having it to 20.

Yup, every morph has their health set to 20

https://imgur.com/a/VlGskoy < Metamorph, Has normal health of mob

https://imgur.com/a/3txJc5c < Changeling, Has health always set to 20, this affects every mob

also the "mob" attack is not even mentioned in the wiki, yet is still a thing in-game, wonder what it does...

Please consult the wiki for how configuration works:

https://github.com/asanetargoss/Changeling/wiki

Health should be calculated automatically for morphs not included in the morphs.json using the base health of the entity. If that is not the case then it may be a bug.

https://imgur.com/a/yH79moN

That is the morph builder menu. Changeling is survival-focused, so if something breaks in that menu, I'm not particularly concerned about it. If you acquire a morph in survival, i.e. by killing a mob, then morph using the survival morph menu, you should see your health on your HUD bar change to equal the health of the mob. That is a feature I would be more concerned of if it was broken.

Meaning of attacks can be discovered from the wiki. Please try looking again.

Oh you mean that particular attack, not attacks in general.

In that case, I don't know, lol.