The Crypt Missile bug isn't fun, it's frustrating on levels 19-21. And the developer said that the bug won't be fixed, so it's 1 out of 5 stars for such negligence.
I Believe there is a bug on the last rainbow at the stage Wizard of Oy. every time I tried to jump on it to get the last pickups I floated it clinging with only the front wheel.
I don't know if it was intentional, but the change in the point of view when the car is at full speed is very disorienting. And it seems that the car NEVER fits in a tight space between two obstacles. Plus, the Invincibility powerup needs a duration meter or something similar. But the game is kinda funny anyway.
Since Challenge Mode doesn't require any player skill other than luck, i guess this is the easiest impossible badge. Indeed a maddening game. But Chtulhu Mythos is supposed to be like this.