After speaking with Mark from Google AdWords, we have clarified that a “decrease bid of 100%” will exclude mobile devices.
This is great news for all those who do not have sites that convert well on mobile devices.
We are waiting to hear back re: tablets and desktop exclusions and will keep you posted.
For whatever reason though, bids between -91% and -99% will not be accepted. You have to either pick -90% or -100%.