Collect 11 Bonus Stunt items while completing Challenge 8.
All gadgets
Intentionally hit 25 Barrels while completing Challenge 7.
All worlds
Find the Hidden Key while completing Challenge 18. The yellow key is in the Mines, across a trestle at the end of a tunnel.
Laser upgrade
Note: You must get an "A+" rank whendoing the following. Complete all challenges, then unlock the "Timer Speed" cheat. Set it to 10% speed. Change the difficulty level to very hard then complete Challenge 18. Get the "A+" rank to unlock the "Laser Upgrade" cheat.
Timer speed
Intentionally hit 13 Detour Signs while completing Challenge 15.
Unlimited ammunition
Intentionally hit 50 Barrels while completing Challenge 18.
Unlimited health
Intentionally hit 179 Barrels while completing Challenge 17.