Here is the full list of all 40 MX vs ATV All Out trophies - there are 26 bronze, 9 silver, 4 gold and 1 platinum.
Win all bronze, silver, and gold trophies
Collect all 100 Sprockets in Free Ride
Place 3rd or better in the All Out Tour
Place 3rd or better in the Pro SX 450 Championship
Place 3rd or better in the Pro SX 250 East Championship
Place 3rd or better in the Pro SX 250 West Championship
Land a jump with a distance of 300 feet or greater
Spend over 100,000 MotoCoin
Complete any Freestyle, any Opencross, any National, and any Supercross
Place 3rd or better in the Pro ATV National Series
Place 1st in any race on All Time difficulty
Ride for over 100 miles
Place 3rd or better in the Pro UTV Opencross Series
Equip as many factory level parts as possible on a vehicle
Upgrade a part to Factory
Place 3rd or better in the Pro Freestyle Series
Pull off 100 stunt combos
Wreck 50 times
Place 1st in every race in a series
Place 3rd or better in the Amateur Offroad Series
Spend MotoCoin for the first time
Beat your ghost in Time Trial
Land a flip
Place 1st in 25 Online matches
Survive the infection
Pull off 5 unique stunts in a race event
Hold a Stoppie trick for 75 feet or longer
Hold a Wheelie trick for 150 feet or longer
Successfully perform a 11x stunt combo
Sucessfully perform any stunt
Successfully perform a 7x stunt combo ending with a no hander stunt
Win 10 holeshots
Infect the most people
Win a Tag Mini-Game
Complete 25 Online matches
Finish a race without going off track
Tune a vehicle part
Place 1st in an Online match with 15 human opponents
Complete an Online match
Lap an opponent in a race