I really enjoyed playing Descent and Descent II, but I hated that $*!%#@ thiefbot in Descent II.
I'm thinking that a thief bot running around the house would be pretty fun. It would like dark spaces, but come out into the open occasionally, or when it's quite dark to steal things. It would use a simple mechanical capture and release with a "loaded" sensor. After stealing something it would move around the darker spaces of a room until it sees its' lair and "hoard" items in it. A while later, it would go out again. I expect I would want this guy to dart around pretty fast, so I'd probably increase the drive speed, so as to make it more of a tripping hazard.
So the rules would be something like:
1) Move slowly and randomly in shadowed or relatively darker areas.
1B) Randomly dart out into lit areas for a short while.
2) Move very quickly in bright or lit areas until a small object is loaded or darkness is reached again.
3) Only steal one item at a time, so be aware of Load/NoLoad condition.
4) When loaded, begin lair sensing and follow dark areas slowly until the lair is sensed.
5) When the infrared lair marker is sensed, navigate towards the lair and engage the mechanical release until a NoLoad condition it achieved.
6) Charge and wait awhile.
7) Begin navigating slowly and randomly in darker areas.
This would sure make my nightly pickup easier. And more fun.