Leveler
Finish ahead of any opponent with an Experience Level higher than yours in an Online Playlist match
This will most likely get done on one of your first races. There is an experience system used in the online mode that tracks your progress. You still get experience even when you finish last making this trophy easier than it sounds as the weaker players, as long as theyve played a race you will be lower than them. I would say again use Off-Road mayhem because if you choose a sport buggy and the others race with bikes then you will be able to plough through the competition. Also you dont actually have to win it, so if a high leveled guy is having a bad race, which is most likely on Off-Road Mayhem because of all the harsh bumps in the roads then you will need to come any position higher than them.

You're It!
Win a Tag Mini-Game in an Online Playlist match
This fun min-game involves racing towards a comedic helmet shaped like a freakish monster and capturing it. The aim is to hold onto it until the 60 seconds run out or chasing down the guy who has it and knocking into him to get it back. There are 3 rounds to play through, finish on top in 2 of them to unlock this. For both of the mini-games you should always pay attention after the game is over to see what the next event is. If its tag and you already have this trophy then veto it and hope other players do to switch it to snake.

Snake in the Grass
Win a Snake Mini-Game in an Online Playlist match
Basically in this mini game you have to knock out your opponent by fencing them in with your snake trail until youre the last one riding. Dont drive into other peoples, or even your own trails or you will be eliminated.