To unlock other cars, you need to
find three keys per level. When you begin a level, it
is a good idea to find all the keys, then complete the
laps. It does not matter what you place when you are
looking for keys; take your time, and complete the
level. If you do not complete the level and found all
the keys, do not worry -- you still get the prize.
However to go onto the next level, you must place
third or higher.
In the third Grand Prix, in the second to last level
"Tomb And Gloom" is where you can unlock the find
fastest car once you have found all the keys. The
third and last key is hidden well here. It is in a
curtain draped off the ground in a descending matter
(just hop of the ledge onto the curtain). A good rule
of thumb when looking for keys is to change the cars
view to a more elevated position, then try to spot the
sparkling keys in the distance.