Here is the full list of all 24 Riptide GP2 trophies - there are 6 bronze, 11 silver, 6 gold and 1 platinum.
All Trophies Unlocked
Smash a bridge in the Factory Shift event
Find the hidden easter egg
Win a race without the rider
Buy 8 hydro jets
Earn 3 stars in every Race event
Get 3 stars in all Career events
Get 2 stars in all Career events
Get 1 star in all Career events
Buy 4 hydro jets
Reach level 20
Earn 3 stars in every Freestyle event
Get 2000 points in a Freestyle event
Get 1500 points in a Freestyle event
Earn 3 stars in every Elimination event
Earn 3 stars in every Hot Lap event
Upgrade a hydro jet fully
Unlock a level 10 stunt
Jump over 200m
Buy 1 hydro jet
Get 1000 points in a Freestyle event
Paint your hydro jet
Upgrade a hydro jet
Place 1st in any event