SONIC FREE RIDERS

As the achievement description implies, you need to get an UNBELIEVABLE Start Dash on every level.

In order to get an Unbelievable Start Dash, you must use the kick dash (kick off with you right foot, like you were riding a skateboard) at the start of the match in such a way that you pass through the Electric Fence JUST as it is going off. You will know if you get it because there will be a message that says "Unbelievable" on the right side of the screen. If you are too fast you will hit the fence and get a BAD, if you are too slow you will get either a GOOD or EXCELLENT.

There are 16 levels in the game (8 Standard, 8 Expert). You will need to get an Unbelievable start at the beginning of each stage. I don't remember for sure, I believe some of the stages are unlocked by playing the Grand Prix Campaigns (there are 5 campaigns).

A good tip for getting the achievements is too try to partner it with another play-through achievement. For example, I did mine while trying to complete each level of Coin Collector.

When you start a level, try immediately for the Unbelievable dash. If you mess up, hold your left arm out 45 degrees to pull up the menu and restart the match. Do this until you trigger the Unbelievable Start Dash. Please note that you must finish the level for your progress to be saved.