Cornfield
Here is a picture of our lod's for the plant. There is an extra lod which was an x-tree consisting of 8 triangles.
What we wanted to achieve with the cornfield was to make it so huge that entering it might be as dangerous as standing in the front line, since you might never be able to find your way out. This demanded a huge amount of cornstalks. Like 60000 plants. Another important thing was that the player was able to see the cornfield from very far away which made our initial approach seem impossible. Another thing we wanted was that the blades on the plant had touch bending.
We realized that the issue wasn't the amount of triangles on screen, but the amount of instances on screen. So we considered making a single object of about 20 plants. But we expected this would give our touch bending some problems.
Then it occurred to us that we could just make the plant with 2 lod's without the x-tree and give it a very short view range like 20 meters. And then have another object consisting of 240 x-trees. This object would be the lod1 of a box which was given a nodraw shader. This enabled us to make the x-trees only start to appear about 20 meters away from the player. We still had to spawn about 60000 of the original cornstalk's and then on top of that we had the patches of x-trees.
In the end, this enabled us to have a huge cornfield with touch bending at a very low performance cost compared to it's size.
In reality the player will never see the cornfield from as high as this, so the border wont be that noticeable ingame.