Here is the full list of all 38 Gas Guzzlers Extreme trophies - there are 23 bronze, 10 silver, 4 gold and 1 platinum.
Obtain all other trophies
Complete the first tournament
Complete the second tournament
Complete all game tournaments
Kill the opponent with a land mine in any game mode
Kill 3 opponents in one race in any game mode
Complete a single race in any racing game mode without being damaged
Kill 25 opponents in total
Kill 100 opponents in total
Kill 10 opponents with a railgun
Kill 10 opponents with a shotgun
Kill 10 opponents with a minigun
Kill 10 opponents with any type of rocket launcher
Kill ten opponents with any type of grenades
Win any race without picking up a health pack
Win a battle race without firing a single shot
Smash 10 opponents in any game event
Die 6+ times in any game mode
Pick up 2 large money packages in a single racing event
Commit a suicide in any game mode
Run over 20 animals in any game mode
Run over 50 animals in any game mode
Run over 100 animals in any game mode
Survive the first wave of zombies in Defend the base or Survivor game modes
Survive the second wave of zombies in Defend the base or Survivor game modes
Survive the third wave of zombies in Defend the base or Survivor game modes
Survive the fourth wave of zombies in Defend the base or Survivor game modes
Survive the fifth wave of zombies in Defend the base or Survivor game modes
Survive the sixth wave of zombies in Defend the base or Survivor game modes
Survive the seventh wave of zombies in Defend the base or Survivor game modes
Survive the eighth wave of zombies in Defend the base or Survivor game modes
Survive the ninth wave of zombies in Defend the base or Survivor game modes
Survive the tenth wave of zombies in Defend the base or Survivor game modes
Kill at least 500 trolls
Kill at least 800 hyenas
Kill at least 1000 fat human zombies
Kill at least 15000 human zombies
Collect 10000 points repairing the base