I'm using the free version and I was able to start capturing after I unlocked the second battle pet slot IIRC. If you still can't, sounds like something is not working okay.
Looks interesting. I'm kinda hoping maybe this will run better than the last Legion pack I tried (that one pretty much required 32gb of RAM, which is fine; just wish they had said something in regards to that). So will look into this one and see about giving it a go. If it requires a lot more...
Curious as well. Guess I'll download and find out!
Edit: it does. The setting is toward the bottom of the Mangos config file.
Edit 2: the option is there in the config, but they don't seem to work?
I was probably about two years younger when we got a computer that somehow ended up my room. I remember my neighbor loaning me Diablo and playing that (I bought the version GOG sells for the memories and to experience Hellfire!). I don't remember the first PC game purchased, but I do remember...
If you haven't already (I know this post is old), check mobs outside of the starter zones because I think in Wrath, they made all the mobs there neutral (changed back in Cata I think... my memory kinda ain't so great!).