Reference article
Gray Tufted Duck’s Race
Gray Tufted Duck offers this race in Swamp.
Entering
Click the local rival and select a duck. There is no level requirement to enter.
Course
Running and swimming. Ordinary races play automatically; trained skills and sufficient energy determine whether the duck reaches the finish.
Winning
Winning gives you 100 coins the first time you finish first. Once defeated, this rival no longer offers the race.
Progression
This race is optional for the tournament invitation.
Rival
This race is offered by 
Gray Tufted Duck.
Original Flash note
Some races give different coin rewards in the original Flash game.