Okay I have been playing around with some NMS code and was able to create my own extended version of a zombie, modify its AI and some other things. Thus i figured I would work on making rabid dogs that run around and attack players, so I went about this the same way. However; I have run into two issues: #1) If the wolf falls from a height where it would normally take damage it crashes the server, I got around this by just cancelling fall damage as a band-aid. #2) I get a NPE whenever I attack the dog it has been attached here: http://pastebin.com/nUEfYMH1 14.02 17:15:31 [Server] INFO at NMS.sdWolf.damageEntity(sdWolf.java:91) ~[?:?] The above line is simply where the code passes the values back to the super.. return super.damageEntity(damagesource, f); At this point in the code, just before control is sent back to the super the values are: 14.02 17:15:31 [Server] INFO Damage source was: [email protected] for: 6.0 so damage isn't null and the damagesource isn't null. Any ideas? Just in case you need it here is my extended wolf class. http://pastebin.com/CseVNJ9N *edit* here's a copy of the crash report when the wolf took fall damage. http://pastebin.com/aeHRqcAn Thanks in advance!