The Rancor curse/vision is given to those who receive a no match in ee wars. They allow you to open the vanished paladin eb and allows you to sucessfully hit it.
In fact, 6 resets gave (and still give?) you the maximum of 550 ally slots. You get 50 slots per reset, and it used to go infinitely high before the reset nerf. Since then the max is at 550 allies.