Here is the full list of all 15 MXGP - The Official Motocross Videogame Compact trophies - there are 13 bronze, 1 silver and 1 gold.
Ride for a total of 300 km (187 miles) in any offline mode
Get enough Experience Points to reach MX Level 20
Get 10 Holeshots in any offline mode
Get pole position and win both Races in a single offline Grand Prix
Get pole position in an offline Qualifying session
Complete one valid race on each track in the game in any offline mode
Get enough Experience Points to reach MX Level 10
Get enough Experience Points to reach MX Level 5
Spend a total of 2 minutes airborne from jumps in any offline mode
Get the Holeshot in any offline mode
Win a race starting from the last position
Enter Replay mode for the first time
Select the Pro Physics setting in the Riding Assists section and complete a valid race
Enter the Bike Set-up menu in the Pit
Complete an Online Grand Prix