We got one too - in the Magic Kingdom in October. It was a particularly quiet day though so we only used it twice - but it's still a lovely momento to have. Everyone in our party was given one - just as we queued to board the train by Splash Mountain.
A Dream FastPass is one of the prizes in Year Of A Million Dreams. It is basically a fastpass that can be used once, anytime on each of the Fastpass attractions in a particular park.
would you believe we just missed getting one on our Dec trip not once but twice! they were giving them out as we got on POC but by the time we got off they'd gone then as we got off Peter Pan they gave the last ones to the family in front of us