Shadow Step Achievement in Sonic & All-Stars Racing Transformed

World tour: Twilight engine cup: Curien mansion

Race as you normally would until you hit lap 3. Now you will notice you get a big air jump and immediately go down into the cellar and get another jump. Do one flip for each and there is 1/10 super combos done.
Now you must drive back up the stairs and do this 9 more times. What makes this annoying is the game automatically sets you on track so you will have to turn around 3 times thanks to the game holding our hand before you can get another combo off. Repeat this for about 5 minutes for the achievement.

Alternatively you can play time trial mode and go around the map 10 times pulling off stunt combos. A good stage for stunt combos would be the Jsrf stage on top of the buildings as you can pull many tricks off near the beginning. Whatever works for you.