Muni is an abbreviation for mountain unicycling, and is a description for the practice of unicycling on any sort of rough terrain. You don't necessarily need a mountain for Muni - it's the terrain that makes it Muni, not where the terrain is.
It is important to lower the seat and to lower the tire pressure. These two simple adjustments make a tremendous difference. Try to keep one hand on the saddle and stand up over the saddle when you go through difficult sections, as this will make it easier to exert more force through the pedals. It is important to have sufficient balance in order to stay on top of the wheel without changing your riding direction too much. The tire will go its own way; you will have to learn to follow it. An excellent exercise is to practice riding a rail. This will force you to stay on top of the wheel without any adjustments in the riding direction.
Big drops may put tremendous stress on the axle if you do them wrong. To reduce the stress, you may roll out of the drop. The point of this is to transform the downward force into a forward and downward force on the muni. To do this you will need some forward momentum as you go off into the drop, and then fold slightly at the waist, and the muni will try to shoot out in front of you instead of getting compressed under your weight. It is easiest to drop from a stillstand, but as you get more confident it is better to just roll the edge into the drop. Try to land with the cranks horizontal and absorb the shock by first flexing your legs, then at your waist and followed by your upper body and arms. If you have practiced hopping in both pedal orientations it may not matter in what orientation you are when you hit the ground, otherwise you can try pedaling the wheel half a revolution or so into the right position before you land. It is important to stand up on the pedals, and it may help to lower your saddle.
It is easiest to roll out a drop on a downhill slope. If there isn't any slope below, you may still use an angled rock or a bump, by aiming for the far side. Try to scan the area below for a good place to roll out a landing.
If you ride in rough terrain with roots and rocks, the tire oftentimes gets stuck behind some obstacle. A solution is to put in a small hop, just enough to clear the obstacle, to regain balance and get going again. Things get more complicated if you are in the middle of a climb. Depending on the riding surface it may not be possible to get going again once you stop. If you are riding in mud or loose dirt, the tire may lose its grip as you put pressure on the pedals. With practice it becomes natural to put in a forward hop to regain momentum every time you start from stillstand. Mounting to stillstand and then doing a forward hop is actually the easiest way to start on a steep hill.
Since it is difficult to anticipate when the tire will become stuck behind something, it is important to practice hopping out of difficult situations in both pedal orientations, that is with either foot back. Also try to practice holding the seat with either hand.
Living in Norway, I have some experience with snow. It is difficult if the snow is deep and if there is ice underneath it, but it can also offer great amounts of fun!
If we assume that there is no ice and that the snow is not very deep, your only challenge is that you do not know anything about the surface you are riding on- where the bumps are and how big they are. This factor makes riding in snow quite exciting.
Riding on tracks made for skiing on is even more fun, because you can ride on top of the snow quite the same as if you were riding on a normal road. It is, however, often a problem to idle or do quick turns as you easily may fall.
Riding on ice, especially ice for ice-skating, is also a huge challenge. You need to sit right on top of your unicycle and do as few moves as possible . If you need to move it should be slow and controlled. Riding on ice is a potential risk to your wrist as you easily may fall backwards.
A studded tire will help you keep in control over the unicycle on ice, see the instructions for instructions on making a studded tire.
When it comes to riding the "Ewok Village," keep these things in mind:
It is possible to ride your unicycle offroad even if it's dark outside with a headlight. This can be a very memorable or even eerie experience if you're all by yourself! With a good light source, the riding itself is not that much more challenging, although it may be slightly more difficult to correctly estimate the size of rocks and other obstacles in the riding surface.
To ride on gravel a cheap LED headlight may be sufficient, but if you want to ride technically challenging singletrack you will need a better light source. Unfortunately a good halogen headlight is rather expensive. Fortunately these can be built at home at a far lesser expense.
A powerful configuration for unicycling features a 20 W halogen light with a 38 degree spread together with NiMH batteries.
Pedal slower and try to carve sideways if possible. Much like skiing.