I want a mindless undead that possesses the considerable cunning of a wolf or other natural predator. I also want something that, while not likely to win marathons, isn't exactly slow and shambling, either. Here's what I've got:
Modify ability scores to be to be str +2, wis +2, and all other ability scores unchanged.
Remove staggered quality.
Add in rule stating they run at x3 speed, not x4.
Grant Perception skill ranks equal to hit dice (still loses all other skill ranks).
Give +2 bonus to Perception checks for keen senses.
Add bite attack (1d6 base damage) as primary natural attack.
Modify disease ability to only require save on bite attack.
Remove death burst ability.
Give improved unarmed strike and improved grapple feats.
This creature, if not under someone's orders, will attempt to hunt and feed upon any living prey it can catch. If successful in feeding upon living prey it heals damage at the same rate a living individual would for the next 24 hours. It can also gain experience points in this manner (equal to what a PC would receive for slaying the creature in question times 2). They can gain extra hit dice, but not character levels, in this manner (they gain a new HD when a PC would gain a level).
These creatures are incredibly tenacious, and nothing except finding an easier source of prey will deter them once they begin pursuit. They are capable of simple tasks, such as opening doors (or attempting to break the door down) and climbing ladders, but not of complicated tasks such as placing a key in a lock and turning it or picking a ladder up off the ground and placing it somewhere they want to go. They do not use weapons. In combat, they prefer to grapple, then bite. They rarely use their slam attack.
Thoughts? Proposed CR? I'm thinking 1 at 1 HD, and by the Bestiary at higher HDs. Is that too low?
I made some minor edits to clarify healing via feeding, increase bit damage, grant a couple feats useful to the creature, and clarify fighting style.