You don't have to reach lap 12 to win the race (however, you won't get the already existing heroic dragon). If you reach lap 15 or just win the race, you'll get the new heroic dragon.

If you get first place by the end of the race and reach lap 12, you'll get both heroic dragons. Laps 7, 9, and 12 will give you a puzzle piece to summon this heroic dragon-you'll need three of them, so do not discard them and be careful so that you don't accidentally do so. To get the already existing heroic dragon, reach lap 12. Usually there will be two possible heroic dragons you can get in a race - one that has already had a race of its own before, and a new one.But you still must reach the required lap or you will not get the heroic. If you're lucky, they won't put much effort into the race, leaving you to win, even if you don't get far in the laps. You will be grouped with seven other people.

Tap/click on it to find out more information about the heroic race, such as what the new heroic dragon will be, the prizes you'll get for each lap, etc. There will be a button which says More Info. Usually at the side of your screen, there will be an announcement for the heroic race coming soon. If it is not there, then the event still did not start. Go to the island with a race track and a dragon in the middle.

Max dragon level in dragon city