To unlock Night Mode for a trial you'll need to complete it in Free Ride first. Once you've done that, you'll be able to swap between day and night on the mountain screen using
or
Each trial has 3 challenges at Night;
Night Rider - Similar to exploration rides where checkpoints are discovered as you pass them (Any Bike)
Beginner - Challenges to complete the course in a certain amount of crashes or fewer (Any Bike)
Free Rider - Checkpoint-less challenges, the same as the Free Ride challenge in the day (Some trials have a required bike)
This achievement is for Crossing all finish lines on the free night mode, which is the last of the challenges listed above. You can't double up on these challenges so you'll be doing each trial at Night 3 times.
My advice for each trial would be to do all 3 of the challenges in one sitting. The first challenge for each trial has no limits on crashes, so use this as a trial run to get used to the track. You will mostly be keeping to the main path as these are generally the safer options, but if you are confident of certain shortcuts then use them to your advantage. The beginner trials have crash requirements but these are quite high and very forgiving, so use this run to refine your route and find the least risky way through the trial which you can run through with minimal risk of crashing. After doing these 2 challenges go straight into Free Rider as you'll have a better memory of your route safely through the trial. Crashing sets you right back to the top of the mountain as with the regular Free Ride. It took me a few attempts on some of them, but generally they weren't too bad if you take it slow and steady. There is some tricky jumps which you'll have to get used to during your beginner/night rider challenges to work out how best to position yourself and what speed you need.
I used the Geronimo bike for a lot of these runs as its a bit more forgiving on jumps etc., but for trials that have a certain bike requirement on the Free Rider I would recommend using that bike for all the challenges so you are used to it when it comes to your Free Rider run.
Info on the challenges is below:
Mountain 1 - GraterhornThis mountain wasn't too tricky, as its the first mountain the trials were generally straightforward. Couple of tricky spots with jumps but use your Night Rider and Beginner runs to get used to the route.
Trial 1: Widows Ravine
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, GRASSHOPPER REQUIRED
Trial 2: Wandering Woods
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, JAVELIN REQUIRED
Trial 3: Rockstairs
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, PACEBREAKER REQUIRED
Trial 4: Ravens Edge
Night Rider - Complete Trial
Beginner - 18 crashes or fewer
Free Rider - No checkpoints, No bike requirement (I used Geronimo)
Mountain 2 - Redmoor PeaksFound this to be one of the trickiest mountains as visibility was quite bad and often got lost when the route wasn't clear. Use YouTube videos if you get stuck on where to go and take it steady.
Trial 1: Sunfalls Avenue
Night Rider - Complete Trial
Beginner - 24 crashes or fewer
Free Rider - No checkpoints, TRAILBLAZER REQUIRED
Trial 2: Summerbridge Road
Night Rider - Complete Trial
Beginner - 27 crashes or fewer
Free Rider - No checkpoints, BOAR REQUIRED
Trial 3: Redwood Falls
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, GERONIMO REQUIRED
Trial 4: Firewood Cliffs
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, No bike requirement (I used Geronimo)
Mountain 3 - Sierra RivieraThis Mountain wasn't too bad for me. Tracks seem fairly straightforward and jumps aren't too tricky to get the hang of. Just make sure you go slow and steady down some of the steeper sections. Trial 3 was the most difficult as the Javelin is very sensitive and easy to crash.
Trial 1: Hell's Spire
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, GRASSHOPPER REQUIRED
Trial 2: Snake's Tongue
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, PACEBREAKER REQUIRED
Trial 3: Red Rock River
Night Rider - Complete Trial
Beginner - 15 crashes or fewer
Free Rider - No checkpoints, JAVELIN REQUIRED
Trial 4: Devil's Cut
Night Rider - Complete Trial
Beginner - 24 crashes or fewer
Free Rider - No checkpoints, No bike requirement (I used Geronimo)
Mountain 4 - Mount RileyI found this mountain actually had really good visibility compared to the others, especially the first couple of trials. Definitely some tricky elements on this one but overall not too bad.
Trial 1: Fiver Finger Lakes
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, TRAILBLAZER REQUIRED
Trial 2: Titan Peak
Night Rider - Complete Trial
Beginner - 24 crashes or fewer
Free Rider - No checkpoints, BOAR REQUIRED
Trial 3: Mistfield Forest
Night Rider - Complete Trial
Beginner - 24 crashes or fewer
Free Rider - No checkpoints, GERONIMO REQUIRED
Trial 4: Storm Ledge
Night Rider - Complete Trial
Beginner - 21 crashes or fewer
Free Rider - No checkpoints, No bike requirement (I used Geronimo)
In working towards completing all of these trials you'll unlock the final paint jobs and outfits required to pop 2 other achievements:
Fashion Victim: Unlock all Outfits
Riding in Style: Unlock all Paint Jobs