Descenders

Complete the bonus objective in the boss level (Skull icon) on Highlands 3 separate times and this will unlock a shortcut that will advance you to the Forest level when starting a new career.

Shortcuts add the ability to select a world to begin a run from without playing from the beginning. To unlock a shortcut, you must complete the previous worlds' bonus objective on the boss track three times. The boss jump doesn't necessarily have to be completed unless the bonus objective requires it. Not all bonus objectives require you to land the boss jump, some are easy just like standard tracks.

When attempting a boss level, simply work towards getting the bonus objective complete and finish the map, then repeat two more times.

(Note: This guide is ONLY for popping the achievement via the HIGHLANDS Boss level.) Like previous guides have probably said, more than just completing the Boss level, you have to complete the Bonus trick in the Boss level three times. (It's probably silly to note this, but you probably still have to cross the finish line after completing all Bonus tricks for them to count, which is pretty easy here because the finish line is immediately after the Boss jump.) The Bonus trick should be written in a green (or yellow (I'm colorblind)) box in the top right once you start riding. My last (third) one (and maybe all of the others) was to complete a 360^o turn while jumping the boss jump. My best tip here that I learned after at least 6 failures is not to accelerate while coming down the dirt road that leads to the jump, as this downward road should give you enough acceleration (without pressing Right Trigger to accelerate manually) from gravity to make the leap over the bridge and land more easily. For each of my failures, I was adding acceleration (using RT) down the dirt road leading up to the jump ramp, which was causing me to veer away from the landing ramp and crash in the grass. You NEED the landing ramp to complete this - the grass will smash you no matter how well you land on it. So just let gravity take you down the dirt road leading up to the boss ramp and it should be enough to take you over the bridge and with no more speed that should make it not too difficult to land after making a 360 turn (I turned right (clockwise) on my final third success). Also, aim for as close to the center of the jump ramp as possible so you do not veer away from the landing ramp. Hope this helps and good luck!