I am aware that StickyJoe19 has already done another guide for this, but that one is pretty outdated, and the record has been significantly improved since then.

Here's what you should do for the best results:

-> In the character selection, choose Peach as your character, as, being a skill type, she has a jumping and technical advantage. (Silver might also be a good alternative.)

-> When you drift you'll get a speed boost. You'll want to keep that momentum going for as long as you can, so as soon as you do a drift quickly get into another one, and try to stay as straight as you can while doing so. When you're on a straight path you'll have just enough room to zig-zag with your drifts. This is why I choose Peach, as her drift builds up extremely quickly.

-> If you drift before a ramp you will go further than usual.

-> When you trick off a ramp you'll get a boost, but if you press B as you land, you'll get even more speed, indicated by a small green circle on the ground. This is especially important at the 3 ramps near the end.

-> Try not to go wide in any corners. You can go wider in the entrance of a turn to get better exits, and be faster, but don't go too far and hit the fences on the side.

-> This strat can save up to half a second, but makes the run quite a bit harder. When selecting the difficulty, choose the hard difficulty. This means the AI will get better starts. What this does is it can give you an opportunity to bump off an opponent when in front of them, which can bounce you further ahead if done correctly. On the other difficulties, they usually don't get a good enough start for this to be possible. Most of the time you'll get a bad pattern where the CPUs will come across and into your path, resulting in a reset. A good pattern however has the potential to save a few tenths of a second. Even with a good CPU pattern, getting the bounce is quite precise. Too early, and you won't get too much of an advantage, and too late, you'll miss the opponent completely and likely slide into a fence, which could cause a reset.

-> There is a trick you can do to take the three jumps even faster than usual but it is extremely precise, and even I can't get it consistently. From the first jump, if you take it just right, then you'll go slightly further than normal, you'll know if you got it or not. If from the first jump you land directly on the Orange part of the second jump, the momentum will carry over into that jump as well as the third, signalling that you got the trick, if not, you'll land just before it and be a little slower overall. If you get it, you'll save a few tenths of a second.

Hopefully with these strategies, you should be able to easily get under 50 seconds within a few attempts.

While I'm on the topic of Snowboard, I might as well throw in Extreme Snowboarding as well, since no one's done a guide for that event.

-> You might think the character here would be the same as normal Snowboard, but that's not the case here. Instead, I recommend picking Bowser, as although his drift takes longer to build up, he is the fastest when going long distances. Also, Bowser is better than Peach at doing an exploit which will be mentioned later.

-> When tricking off of ramps do 1 backflip/frontflip and 1 spin. This combo fills up the "trick gauge" the quickest when not boosting, but when boosting, just do backflips/frontflips.

-> This event is heavily dependent on RNG. Items wise, you will want to hope for as many Barriers or, even better, Stars as possible. If you get a Boo or Bomb, discard it immediately as it would be useless to you. Use a Barrier item immediately for protection. If you get a Star, I'd recommend holding onto it until you see an attack heading your way. Through my testing, you can't get a Spiny Shell, Red Shell or Chaos Emerald in first place. Once you get in the lead, Bombs will be of little concern to you. Your main worries will be Shells, Boos, and Chaos Emeralds. You'll want to hope for as little of these as possible, as those will be pretty big hindrances to the run, potentially making you lose several seconds through no fault of your own.

(Boos will drain the trick gauge, resulting in you not being able to use as much, as well as stealing an item if you are holding one, while Shells and Chaos Emeralds will slow you down. The effects of Shells/Chaos Emeralds can be prevented by using a Barrier/Star, Boos can only be stopped by a Star.)

-> This is what I was referring to earlier. The first place where you can do this is at the split with the big jump. Take the right path. Aim for inbetween the middle cone and the cone second from left, and as you're about to hit them, use your boost and go as far left as you can. This will give you the optimal speed and position to boost into the rail on your left.

The second can be done about half way through the course where there is a split in the road with a chain chomp in the middle. Go left here and get past some enemies. Then, as the rail on the right ends, boost into it and you will be zipped forward quicker than usual, which could save several seconds per lap if done perfectly.

Not necessarily a tip here, but I noticed that if Boo steals from you as you're getting an item from the roulette, it will steal the last item that appeared, rather than whatever you were going to get. (Say you were going to get a Barrier, and a Boo is used. If the last item you saw in the roulette was a Spiny Shell, it will actually steal the Spiny Shell, not the Barrier item.)

You should hopefully be getting times under 2:40 by using these. And that concludes my guide.