Sign in to Marriott.com in order to be able to see the promo and register:
https://www.marriott.com/rewards/promotion.mi?promotion=FB18

• Stay at any of our participating hotels and resorts worldwide between September 26, 2018 and January 31, 2019.
• Earn 2,000 bonus points on all stays* of two or more nights and 1,000 bonus points per brand, starting with your second brand.
• Play our game 29 Ways to Stay from October 11 through November 8 to learn more about our 29 brands and for the chance to win prizes, including points and free nights.**
• Register by January 7, 2019

Nights spent while redeeming an award are not eligible for bonus points.

Finer print:
*A 'stay' is defined as consecutive nights spent at the same hotel, regardless of check-in/check-out activity.

Registration is required. Marriott Rewards, Starwood Preferred Guest, and The Ritz-Carlton Rewards (“Loyalty Program”) members who register for this promotion by January 7, 2019 will earn 2,000 bonus points per stay on stays of 2 or more nights at participating brands. Plus, members can earn an additional 1,000 bonus points per brand starting with the second brand at which the member stays during the promotion earning period. The promotion earning period is for stays between September 26, 2018 and January 31, 2019, at participating Marriott Rewards, SPG and Ritz-Carlton properties. A 'stay' is defined as consecutive nights spent at the same hotel, regardless of check-in/check-out activity. Rooms booked through most third party online retailers and select travel agency bookings are ineligible to earn for this promotion. The member receiving this offer has been targeted and the offer is not transferable. Bonus points will be awarded to the member’s account up to six weeks after the promotion ends. Marriott Vacation Club® owner-occupied weeks are not eligible for bonus points and nights spent while redeeming an award are not eligible for bonus points. Only one room per hotel is counted toward a member’s nights or stay. Members electing to earn miles are not eligible for this promotion. For a list of current participating brands, visit https://www.marriott.com/loyalty/earn/hotels.mi. All Loyalty Program terms and conditions apply. See https://www.marriott.com/loyalty/terms/default.mi for more information. Visit www.Marriott.com/MorePlaces or call 888-MARRIOTT (888-627-7468) for complete details.

Clarification from Starwood Lurker in post 125:

1. In regards to the part of the offer where you can earn 1,000 points for trying a new brand…There is no minimum length of stay, but you only earn it starting with the second brand. So if you only stay at one brand during the promo period, you will not earn this bonus. But if you stay at 2 or more brands, you will earn 1,000 points for each of those brands after the first one even if the stay is only one night.
2. You earn on every stay of 2+ nights, so it isn’t about accumulating nights. If you have two stays of 1 night each, you will not earn a bonus. If you have two accounts, you may register for MegaBonus with either or both accounts. You will only be able to earn with one account at a time because you will earn the bonus points in whichever account the stay was booked with. Example: If you have two accounts that are not combined: If you register for MegaBonus with your SPG number and stay with your SPG number, you will earn the bonus points in your SPG account. If you register for MegaBonus with your SPG number but book your stay with your MR number, you will not earn bonus points.