The new Disney Crossy Road Moana Update from November 2016 was just released. If you have any tips & tricks how to unlock the remaining secret characters, please write us comments here!

NEW  #1 Frog Monster - Heroes of Mota Nui Set 
Get the characters Moana, Maui, Hei Hei and Pua to unlock the Frog Monster.

NEW  #2 Chicken Feed - Action Unlock
Play as Hei Hei and collect 25 chicken feeds. 

NEW #3 Gramma Tala's Ghost - Action Unlock
Play as Grammy Tala and die 25 times.

NEW #4 Maui's Hook - Action Unlock
Play as Toddler Moana and find the fish hook within the level.
 
NEW #5 Toddler Moana - Daily Missions
Get Toddler Moana through Daily Missions
 
NEW #6 ??? - ???
The unlock is not unknown. If you have any idea, tell us in the comment!  
  
Special thanks go once again to YouTuber DaMobile Mob for providing a lot of the info!