What is that horrible sauce/dressing on the new M Burger from McDonalds? Did You Like It?

I have not tried the NEW 'M' Burger ! I have been told that it is so DISGUSTING ! Apparently the Sauce is for a Special 'Period' ! I have not been told how long that 'Period' is on for though ! I think that it 'comes on' once a month ! Your guess is as good as mine !