Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Mantis LOD Editor – Professional Edition Free.
Mantis LOD Editor – Professional Edition v6.2
Mantis LOD Editor Pro is a polygon reduction toolset (include an editor extension, a command-line tool, a standalone app, a progressive mesh generator, and a progressive mesh runtime), you can simplify your meshes and make LOD from within Unity’s editor, or from the command-line tool, or from the standalone app.
Most important, the toolset can generate high quality LOD with very low triangle count, this is very important for mobile games.
This product can run both on Windows x86_64 and macOS.
This product contains the world’s first commercial progressive mesh technology for Unity!
What’s progressive mesh technology? In short, it is an advanced automatic LOD technology, you no longer have to make LOD manually, and your game will run more smoothly and has hardly no pop up effect.
The generated progressive mesh support all platforms, make once, run anywhere!
This product support Unity 2017.4.0f1 and newer versions!
• Provide all source code of the plugin.
• Generate LOD for both static meshes and skinned/rigged meshes.
• Automatically protect UV boundaries and material boundaries.
• Protect all open boundaries or smartly merge some smooth parts of open boundaries.
• Preserve all blend shapes.
• Super fast, it can simplify 50,000 triangles per second.
• Preview final effect in real time.
• Can simplify huge 3d models.
• Simplify hundreds of 3d models in batch.
• Advanced progressive mesh technology.
• Generate progressive meshes for hundreds of 3d models in batch.
We provide you a free trial edition on our web site , feel free to evaluate our products with your own 3d models.