According to the announcement, the new contest will use 5 heroes instead of the usual 6, with one only available if you were a top spender or have opened numerous gold chests (less than 1% chance).
There was also special emphasis just recently that the new heroes are now available in the gold chests.
Devs may think they are clever reducing the number of heroes you can use by one to force some players to spend some money, but they disgust the most of us instead and more and more people are quitting the game. Way to go, thinking up such petty schemes instead of focusing on the really important directions that will gain players goodwill. As resentment builds, it will be too late to reverse it.