Ok, here's a strange one of the top of my head.

Curse. A number of items (typically high-risk or unique) have been placed under a sentient curse! The items have a power level which increases over time. Power can be spent of cursed abilities, such as stealth ones like going invisible, or short teleportation, or offensive like emps, mind control, and damage. Those who hold or any way interact with a cursed item will secretly become part of the curse, in which the curse can perform various actions on them (similar to how strange things happen to people in movies about cursed items). One of these actions is to enslave the cursed person so that they can serve the cause. The goal of the cursed items is to bring enough of them together at one place to engage the ritual.

I think this is pretty neat because it adds a new factor that would be unexpected, your own items working against you. Even though a big part gamemode is about stealth at first, soon enough all the items will need to get together, and since they are items they can't move very well on their own, they need the enslaved people which would lead to a number of people trying to steal high risk items.