What's the worst thing player can do with DM permissions?

Hi! I’m considering giving one of my players DM permissions to run Clash at the Kobold Cauldron for our table. What is the worst thing they can do with DM permissions but without access to the Forge API? What is the worst-case scenario? I’m sure I’m overthinking this but better safe than sorry.

Most things are going to be isolated to the world they have GM permissions so make a separate one for them for sure. They could do things to drive up your data quota though such as embed large images in journals or import 1,000’s of actors or items into the world.