Players can gain more than 2500 ranking points - cups by winning duels.
Winning duels will let you gain more cups but every 2 weeks all players who have more than 2500 points will have their points set back to 2500 and the surplus of extra points above that number will be divided by 2 and the result will be added to their Legendary Trophies points. For example, if a player finishes a season with 2600 points, he will receive 50 Legendary Trophies points in a result - 100 points as a surplus divided by 2 will result in 50 points.
Your current Legendary trophies points can be viewed on your Profile.
There are currently no special rewards for gaining Legendary trophies.