In default world i get crash log:

url - http://pastebin.com/FSEvc4WA

I haven't had this crash, and I think @krwminer said ayeracos are fine in the compiled version, so I'm not sure what the problem is. We can't really trust crash reports from cauldron servers though, since cauldron modifies a lot of stuff.

hmm, but is it right, that we can summon horde ( by horde horn ) in main world ? ( not in ender ) and if i hit him - forge get crash..

In main world in this chunk ( where is entity horde ) get`s crash, this is not cauldron crash, it only crash client not server...

with spawning boss in ender no problem, but after 1 hit...

I did not experience a crash with the ayeracos when I spawned them in the End. They did act funny about not coming down. I was not sure if it was a creative mode thing.

I did not try spawning them in the Overworld. That should not be allowed as far as I know.

Sense no one else can reproduce this, it's probably a conflict with another mod. Does it crash if you remove all your other mods?

I tried this again. It did not let me spawn them in the Overworld. When I did spawn them in the End they worked fine. The only thing we may want to fix is that it is easy to get them to get stuck in endstone and suffocate. (I am adding a separate Issue for that).

Closed until it can be reproduced.