I had a similar problem, I wanted to make curtains in a doorway. A sprite decoration was out of the question, as it rotated towards the player. I tried to make a single plane with texture and import it as a model, but for some reason it made decoration entities (like the barrels on my screenshot) on the other side invisible, whether the transparency option in model configurator was used or not. After a LOT of trial and error, I came up with a way that seems to work. Can be used for things like fences, perhaps even wall decals.
So, here's the weird procedure, maybe someone will find it useful for their projects:
1) I made an image of the curtains, 64x64pix png with transparency.
2) Used a voxelizer tool on this site https://drububu.com to convert it to 64x64x1 voxel image, then save it as .vox file (MagicaVoxel format)
3) Open it in MagicaVoxel (it's a free software), export it as .obj file.
4) Open the .obj file in Maverick Model 3D (another free software), export it to .md3 - it's important to DO NOT touch anything, don't move, don't scale, nothing - otherwise texture will be corrupt.
5) Import the .md3 file to EasyFPS, set Y offset to 3, scale to 4. Do not merge with level geometry, because it will be halfway in the ground and the offset won't work for some reason.
And yeah, there's an ingame model with pixel-perfect texture to the original png and working transparency. Offset is tiny bit off, but the engine does not take inputs with decimals like 3.1 in offset field for some reason.
