I decided to make felted playmats for my cousins' children. These are really just basic flat felts with a few embellishments, but I thought I'd post them here with some tips on making these things since I've been making this sort of thing for a while. This assumes some familiarity with the wet felting process, easily found in any number of places on this board or elsewhere on the internet.
Two finished mats:


I'll post some photos of the first mat in progress.
When I want to add a lot of details with a needle, I will work these felts on a large piece of foam. I lay out the fibers directly on the foam like usual for wet felting. Since I want these mats to be sturdy, I used 5 layers of fiber. The first three layers were in some grey fiber, then the two layers on top of that have the background colorway for the design. If you just use one layer of the top colors, the bottom layers will tend to show through too much.
Here is the fiber laid out in five layers:

The background grid is in inches, so you can get an idea of the scale here. Another tip is that if you use a single color in the background, your design will look flat or cartoonish. Here I've used two colors of blue in the sky, and some art batts and tufts of other colors for the ground. If I were doing an art felt and not a playmat, I would have used the background colors through all the felt layers (or at least something in the family, like some kind of blue in the sky region and a brown or green in the ground region). I'd also have done a more careful job of blending the sky fiber colors and used more intermediate tones. But playmat = using up excess fiber in certain colorways. This will still look somewhat cartoonish, but way less flat than if I used only one sky color and one ground color.
At this point, I take a multi-needle tool and lightly felt down the whole thing to keep the design in place. This is a good point to start edge control, working the edge a bit with the needles.
Now I want to add mountains. For anything that is going to have a sharp edge, I want to use a prefelt. If I wanted to have a clean sky/ground edge, I would use a prefelt for the ground. In this case, that edge will be mostly covered with other designs. This is the prefelt that I used:

This was made from some natural colored fleece. It has been laid out and partially felted just to the point where it can be handled and cut into shapes, but it is not tightly felted. I cut out the mountain shapes, and put white locks at the tops for snow. Wrapping the locks to the back of the prefelt is helpful. I lay the prefelt onto the fibers and needle felt it until it starts to stick , especially around the edges.
(camera batteries needed to be recharged, no pics of this process)
Now I start to lay on texture: clouds, locks, 3d-elements made from prefelt. I added a bunch of curls, locks, and neps to the ground area and also a 3-d cave. The cave is made from a piece of prefelt, needled along one edge with some locks to cover up the border and help it adhere.

Warning! The foam pad and fiber are major feline attractors.

Tip: The best way to extract cats is to try to take their picture, causing them to immediately vacate.

Anyway, here we are with some embellishments.

Now I add the topmost design, in this case some trees:

And then needle everything down until the felt can be peeled off and carried around. At this point I wet felt the whole thing, taking care to keep it rectangular and flat, and not to felt the whole cave into the background (plastic bags can help with that). After felting, wash, rinse, soak in water with vinegar, and lay flat to dry. Then press with a hot steam iron. All done!
For the other mat shown at the top, there is a cave that is hard to see, and I also made some small wet felted "boulders" and needled them on after finishing the rest of the mat.
