What is the Mietpreisbremse?

This is a rent brake - theoretically it is a legal mechanism which can be used to get a rent deduction or refund from your landlord if you can prove that they are charging you significantly over the Mietspiegel for no good reason (i.e. no furniture, no renovations). If you are a member of a renters’ union, they can help you work out if you have the grounds to enact this mechanism on your landlord. http://capitallanguagesolutions.com/en/mietpreisbremse/