Overview
Estimated Trophy Difficulty: According to some....about a 4-5 out of 10. Not sure I agree with this..but oh well.
Offline: 23
Online: 2
Approximate Time: Depending on your skill and patience...you may finish this in 5-10 hours. I...however...did not.
Minimum Number of Playthroughs Needed: 1
Missable Trophies: None I know of
Glitched: Pack Rat...maybe, not positive
Cheats: None I know of
Road Map
To start with...find a boosting partner and get the 2 online out of the way. Send your partner an invite to get "Friendly" out of the way. Then during your game...constantly slam your opponent to get 20,000 stunt points. Once you have 20,000 points...find a hill and do another "trick". Once you have landed that "trick"....Online Acrobat should unlock. I had about 21,000 points and then had to do another trick to get it to unlock. One little detail a lot of guides seem to leave out.
Next...start your Career game. Try not to buy any snowmobiles or parts as you are working towards Stingy. You will need to earn and have on-hand $50,000 to unlock Stingy. Try to place first in each race....to unlock your outfits and other snowmobiles. You don't have to place FIRST in each race, as some items only require you to place in Third...however,it is probably better to just work on getting first. Halfway through Career mode..you will unlock Hoarder....and at the end you should unlock Pack Rat. However...Pack Rat didn't unlock for me at first as one of the snowmobiles didn't unlock for me. I had to go back to that one challenge after the game was over to unlock it and get the trophy finally. You don't have to run the last race...or at least I didn't as I made sure to come in first during all other races.
There are a couple of challenges you have to beat under 2:30:00. Which means you have to finish the challenge with at least 50 seconds still on the clock as the challenges start you at 3:20:00. For most tracks...the Summit snowmobile is the best since it has the best grip.
Local co-op....just fire up a second controller and make sure you don't have any computer opponents and get Roadrunner out of the way. You could do this during your career playthrough...but it is much easier to do it this way. This is also a good time to get Woodcutter done as well.
Stunt clean-up...You will probably get most of the stunt's done during your career mode...at least I did, so this is a good chance to get those last few nasty trophies out of the way.
Map: Whitehorse XC
Snowmobile: MX Z Renegade 1200
Character: Jack Yapp or Ingrid are both good for these.
Competitors: 0
During this race...about halfway to 2/3rd's of the way through the race, you will come to a big hill. Some people seem to think this is a cliff...looks just like a hill to me...anyways, this is where you want to work on your flips. You will want to have a full boost meter and race up this hill. At the top...hit
to give you a heighth boost and start your flips.Stay airborne for 2 seconds for Big Air and 5 seconds for Orbit.
While holding L1...pull back on the left stick for Backflip and Double Backflip
While holding L1...push forward on the left stick for Front Flip and Double Front Flip
Do a stunt combo with the left stick for Acrobat (2 stunts) and Wire Fu (3 stunts). I however had done these during the stunt challenges during the career mode.
Hangtime (2 seconds) and Frozen (4 seconds) should unlock during your flips. Once again...I had done those during Career mode.
One note about the flips.....you WILL NOT unlock BOTH trophies for doing a Double flip. You will only get the ONE trophy for doing a double flip. You will have to do EACH flip seperately.
Trophies:
Bully 
Take down one opponent.
You should get this once you take-out one of the computer opponents.
Acrobat Perform a 2-stunt combo.
Simply do one stunt, release, and do another stunt before you hit the ground.
Adrenaline Junkie Stay in Adrenaline mode for 30 seconds.
See Boostaholic..harder then it sounds.
Hoarder Unlock half the unlockables during Career mode.
Unlockables are your snowmobiles, outfits, and videos.
Hangtime Hold a stunt for 2 seconds.
Big Air Stay Airborne for 3 seconds.
You should get this pretty early on since some of the hills are pretty high.
Backflip Do a backflip.
Hold L1 and pull back on the left thumb stick.
Frontflip Do a frontflip.
Hold L1 and push forward on the left thumb stick.
Woodcutter Collide with 3 trees during a race.
Not sure EXACTLY how this works as I slammed into more then 3 before this one unlocked. So make sure you got some speed before running into any trees...and keep running into them until it unlocks.
Crowdsurfing Collide with the crowd.
Really easy as you will probably get this without even trying...sheesh...I did. First time I went over a jump....WHAM...right into the crowd. DING.
Friendly Invite a friend to a race.
Roadrunner Start and finish a race in first place.
Easiest to do with a co-op partner...or just with a second controller.
Berzerk 
Take down 3 opponents without crashing.
Knock off computer opponents or beat down a friend without crashing.
Pack Rat Unlock all unlockables during career mode.
If you did all the stunt challenges correctly..this should unlock once you get to the final race. You don't have to run the final race. This didn't unlock for me even though I had done all the challenges. I had to go back and do the Air-master challenge again to finally get the last snowmobile and get this trophy to unlock. So..I don't know if the game or trophy glitched on me...so make sure to keep an eye on your items as you go along.
Stingy Collect $50,000 in career mode without spending it.
Not to difficult, just make sure you have $50,000 on you and this should unlock.
Frozen Hold a stunt for 4 seconds.
I did this during the stunt challenges...just make sure to release the stunt before you hit the ground. Hold L1 or R1 and choose a stunt with the left thumb stick.
Untouchable Win a career race with your sled intact.
Just make sure to finish a race without crashing. You will probably lose a side panel or two during the races...just make sure to not CRASH.
Head Splat Land on top of another player during an offline match.
Some people say to do this during a co-op match....I did it during career mode after coming off the second jump and landing on a computer opponent.
Rampage 
Take down 4 opponents without crashing.
Just like Berzerk...only 4 opponents. Can be done during career mode or in an offline game against a friend.
Wire Fu Perform a 3-stunt combo.
Just like Acrobat..only you have to do 3 stunts. Hold L1 or R1 and use the left thumb stick. Try to find quick stunts like Superman and do it 3 times.
Boostaholic Stay in Adrenaline mode for 60 seconds.
Harder then it sounds....believe me. This and Adrenaline Junkie were my last ones to get. Find a stunt track...the one I used was one of the Russian ones. Preferably one with a big hill with a long line for your landing and to pick up speed. To get into Adrenaline mode...do stunts until you meter is filled. Hold down the
button to boost. Now comes the tricky part. Make sure you go BACK and FORTH OVER the same hill to keep yourself in the air. While in the air...CONTINUE to do stunts to REFILL your meter. When you land....spin around with your 
and go back over the hill and do another stunt. One more thing....when doing the stunts, try to do the same stunt over and over. You will lose 50 points for repeating the same stunt. Also try to land either on your skids or the back end. You will lose 50-70 points for not getting a Perfect landing. Of course...this little detail was left out of other trophy guides. Thanks to Roughdawg and Shoe for giving me this little tidbit. Otherwise...I might still be trying to plat this game.
Orbit Stay in the air for 5 seconds.
The Whitehorse XC has the largest jump in the game and you will probably get this the first time you fly off that jump. Remember to hit the
button when you get to the top for that little extra UMMPH.
Double Backflip Do a double backflip.
See Double Frontflip. This one is much easier then the front flip.
Double Frontflip Do a double frontflip.
Try to do this off the Whitehorse XC jump. Make sure to boost your way to the top and hit
once you get there. It is much easier to do with someone that has Excellent strength...as they make the sled flip faster. The sled will probably rotate while your spinning...so try to make sure to correct that before you land. You don't have to make a PERFECT landing...but you still will have to correct your spin as you get close to the landing. Took me several tries before I was finally able to land without nose diving.
Online Acrobat Get 20,000 stunt points in a single online match.
By far the easiest way to do this is co-op with a friend. Make sure to run into them and crash them repeatedly to earn 300 points for each take-down. Some people say this takes 20 mins...the 3 times I did this with friends...took about an hour each time. Once you get to 20,000 points...find another hill and do a stunt to unlock this trophy.
Platinum 
Unlock all other trophies.
If you made it this far and finally unlocked this nice shiny plat...I congradulate you.
