Here is the full list of all 17 Demon Truck achievements.
Begin and end a boss battle with one heart remaining
Defeat 666 enemies
Boost for 6.66 continuous seconds
Equip 5 Hellgunz in one run
Vanquish 6 bosses
Vanquish 18 bosses
Vanquish 66 bosses
Run over 666 enemies
Boost through 666 obstacles
Complete 16 waves in one run
Destroy 6 enemies with one tossed clown
Equip 3 Clown Tossers in one run
Clear wave 5 or higher without firing your weapons
Take 3 shots from the same laser scorpion
Select the left hand upgrade 6 straight times in one run
Defeat 66 rivals
Earn 100% Score Bonus in one game