Just called the Marriott Rewards today and got signed up for a Platinum Challenge. Need to hit 18 room rights until end of April.
It is different from 9 stays usually found here, before that I send a message to Twitter@Marriott, they also told me 9 stays, so just wonder is the offers are difference from countries.
They told me it is better to hit the target after end Jan then the status will last until Jan 2017, very good deal.
By the way, 18 room nights is more easier for me, and my status is still GOLD until I make the challenge, so let's see.