How to play Co-OP LAN:

Download Steam (http://store.steampowered.com/about/) and make an account if you have not done so.
Then make sure steam is completely closed (via taskbar) and

download a hacked steam aka Green Luma (http://cs.rin.ru/forum/viewtopic.php?f=29&t=57895/) extract it into the stream directory.

Then download a Lan cracked exe: http://minus.com/lbrRAbSOnjuEnD

Then run Orcs Must Die 2, it should let you invite steam friends.

In order to add steam friends: have them add you or buy a 99 cent game: http://tinyurl.com/9qbqfhy so you can add friends.