Similar to grass blocks and mycelium, nylium decays (immediately on a random tick) into netherrack when an opaque block is placed above it. However, unlike grass blocks and mycelium, it does not decay underneath water and lava.
can someone PLEASE upvote all my Minecraft dungeons papercrafts https://minecraft.gamepedia.com/Nylium
1. Click on the papercraft design image.
2. Make sure it has not been resized by your browser (you might need to click the image again).
3. Print using your browser's Print function.