I'd love to share some techniques, tips, and tricks I used to make Fast & Faeries (general techniques and plenty of Unity-specific items), a furious and frantic racing game between miniature forest faeries.
Play now if you have not seen it yet:
https://ldjam.com/events/ludum-dare/38/the-fast-and-the-faeries
How it's made (Unity):
Proc-Gen Ground: The ground is procedurally generated in 100x100 unit meshes using Perlin noise to shift each vertex randomly but consistently so that other proc gen ground meshes can line up with it. Several levels of Perlin noise of different frequency are added together to create larger features (smooth hills) and smaller features (bumps). In Unity, use the Mathf.PerlinNoise function to generate Perlin noise. This ground mesh is also used in a mesh collider. The ground is generated on the fly, up to 300 units further ahead than the leading player and up to 200 units to the side of each player, and is recycled 300 units after the last player. Dandelions and trees are then randomly placed onto each ground mesh.
What a naked ground tile looks like in the editor in game after some proc gen, looking only at the ground layer:
Race Trail: The yellow center trail is generated on top of the ground by using raycasting to see the height of the stones. The trail uses a few sine/cosine waves as well as some Perlin noise to see what bends there should be. Trail boundary mushrooms are added to the left and right sides of the trail the same way. These markers are pooled to that they get reused. The side markers actually contain box colliders that reach towards the previous marker so that the players cannot go past them. When the center markers are generated, they check around themselves for trees, and push away any trees in their radius so that the center trail is somewhat clear. (physics layers and Physics.CheckSphere() in Unity)
*Curly Vines/Trees: * There is only one model for the trees/vines, but it looks different depending on how you rotate and scale them. Spiral/vine-link shapes blend together to look quite organic. A pool of trees/vines is generated. Then the trees are populated along the sides of the trail as a hedge wall using that pool. Using a Unity 5.6 instanced shader greatly speeds the performance of these trees, drastically reducing the draw calls.
Particle Trees: At the start and end of the race are thick areas of trees/vines - these are generated using a particle system which simply displays meshes rather than billboards, with varying scale and 3D rotation.
Dandelions: I experimented with a few ways of making the dandelions, but ended up making each dandelion a particle system of dandelion seeds that rests on a dandelion stem mesh. I had to custom position the dandelion seed particles using the Fibonacci Sphere layout to make them evenly distributed. Adding a trigger collider to the head of the dandelion puff allows a script to give the particles a velocity when hit, and gives them each a random color.
Fog: Linear Fog at a far range of 300 units greatly helps hide the fact that the camera can only see 300 units ahead, and helps to blend the far trees into the background.
Far blurred foliage: There is a particle system of glow particles that follows the position of the camera. The particle system emits these blurred colored glow particles on the shell of a sphere right before the 300 distance of the camera. This gives the effect of out-of-focus foliage that is moving around.
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Fog: Linear Fog at a far range of 300 units greatly helps hide the fact that the camera can only see 300 units ahead, and helps to blend the far trees into the background.