Rule 1: You have to build 2 dueling coasters of either the same or different ride types! Making two coasters on top of each other which share the same track like this tutorial is also allowed: https://youtu.be/pHppVm9DH1A
You are not allowed to use extra stations for these coasters to let more trains synchronize with each other.
You have to build 2 dueling coasters, no mobius track, no extra dueling tracks.
Rule 2: The two rides must interact with each other several times throughout the track, and should not only be near each other during the chain lift section. Mirrored rides are not allowed. Try to incorporate some near misses, or interlocked inversions, or let your coasters race each other!
Rule 3: The dueling trains must arrive at the station at approximately the same time (when both are full).
Rule 4: Maximum map size is 50x50!
Rule 5: No custom scenery, objects or rides! You are only allowed to use objects from the base game or the official expansions.
Rule 6: You can add 2 extra functioning tracked rides, like a miniature railway or a rollercoaster, and 3 extra functioning rides with a base, like a merry-go-round, a maze or a launched freefall tower. With functioning ride, I mean a ride that is either opened or in test mode. For an extra challenge (not required) you could also make your extra tracked rides duel with each other.
Rule 7: Unlimited trackitecture is allowed, but you cannot add any extra functioning rides this way, just track pieces! You are allowed to temporarily open them if you want to spawn a stationary vehicle, for example. These rides have to be closed when you submit the map.
Rule 8: Have fun!

Contest parks

Showcase parks

Duelling Coaster Contest

Multiplayer Round 21

Multiplayer Round 35

Multiplayer Round 22

Multiplayer Round 30-1

Multiplayer Round 20

Bamovich