I happened to glance at my promos page today. In addition to the progress tracker for the current MegaBonus, in the New Promos section there was a blank box with no title and a Register Now button. Of course, I clicked on it. It brought me to the following page -
https://www.marriott.com/rewards/pro...promotion=MZ18 - with a vague "Earn with every stay" message and nothing else.
Now I have a second progress tracker counting towards 50 Nights - still no description of what I'll earn, end date, or anything else.
Unfortunately I don't have any stays booked in the next few weeks to test this out.
Any guesses?