Descenders

This is one of the hardest achievements in the game. Luckily, not all 5 worlds have to be done in one run and can all be done individually. The first tip I can give you is to practice with seeds 1001 through 1005. They don't give achievement progress, but it's better to get accustomed to the tracks here than waste up to 40 minutes on a run, go in blind and fail. That being said, let me explain.

Bonus worlds are identified on each map from Highlands to Volcano by a star, usually on the edge of the map and opposing the boss jump. Another ~easy~ way to pinpoint their locations from afar is looking at the player count on tracks. These tend to have a higher count as people are stuck there longer. You have whatever lives you bring into the track and you HAVE TO complete the bonus objective on the track THEN ride through the finish line for it to count.

The first bonus world is Construction Site on Highlands. This is one of the hardest ones of the bunch and requires you to reach the top of the construction site without crashing. There's a bunny hop early on that is the hardest obstacle here. Use Y to switch between camera angles to toggle between first person and the default camera to place yourself.

The second bonus world is Mega Ramp in Forest. The best way to do this (via Maka91) is to begin with a front flip + trick, get a clean landing, hit the first ramp and do a triple backflip + trick, then hit a 540 + trick on the second ramp. If you're still missing points, try and carry the momentum back to ramp facing you and backflip off, even extend with some 180's if need be.

The third bonus world is The Ranch in Canyon. Best tip I can offer for this one is starting earlier in the run and trying to get the sped up rotations perk. Superman = down on right stick + LB. No Hander = up on right stick + LB. Can Can = diagonal down/left + LB.

The fourth bonus world is Moon in Peaks. This is probably the easiest one as long as you have good control of your bike and the physics.

The fifth and final bonus world is the real challenge. This one is Kids Room in Volcano. My biggest tip for this one is having the improved bunny hop perk. Remember to keep an eye out for player count, if someone's out this far and out on the very edge, there's a good chance they're in the Kids Room. The biggest pain about this one is it requires you to reach the Volcano. To reach the Volcano, you have to complete the fire node and fire ring boss jump for each region from Highlands to Peaks. Once in Volcano, you have to find the bonus world like any other. Once again, use seed 1005 beforehand to practice because one of the toys you need to collect is unbelievably difficult. Ride the left ramp down, carry your speed all the way to the far back of the room, ride up the massive ramp from bottom left to top right, bunny hop onto the wall, bunny hop off the wall over the log and into the toy. It's damn near impossible normally but I got it within a handful of tries with the bunny hop perk.

Here's a clip by Maka91 which should help a lot as it's much more compressed than mine was. https://twitter.com/PMaka1991/status/1128152464199487489

Good luck. This one is not easy nor fun.

There are five bonus levels in Descenders which are found in the four standard Career worlds and the one hidden world Volcano (see below on how to access Volcano world). They DO NOT need to be completed all in the same session. Once a bonus level is completed successfully, you will gain access to the level in freeride which makes it easy to keep track of which ones you have already done if you forget. The bonus levels are as follows:

Highlands: Construction Site
Forest: Mega Ramp
Canyon: The Ranch
Peaks: The Moon
Volcano: Kids' Room

The bonus levels on each world map are always located on the outer perimeter of the map and are often out of the direct route to the boss jump. Explore the edges of the worlds until you find the bonus track. If you notice a red circle with a number on an uncovered track on the edge, that is likely the bonus world (it indicates the player count on each track, and players seem to congregate on bonus worlds).

They can pose a challenge, but they are easy if you know the right techniques. The hardest part of this achievement is getting to the Volcano world to even get access to the Kids' Room bonus level - you'll need to complete all fire node tracks on each world and jump through the fire ring on each boss track. Only then will you travel to the Volcano after the Peaks boss jump.