A powerful, easy to use, non-destructive Mesh and Material Merger Tool.

This tool makes it possible to combine groups of objects into a single or small groups of objects in order to improve the performance of your games without sacrificing your workflow.
It also allows for the creation of merged LODs by re-using already existing LODs from the original objects, and controlling the percentage of objects included in each LOD and minimum size each object needs to have for each LOD.

Manual: Advanced Merger Toolkit Manual

Features:
- (NEW!) Supports Skinned Meshes!,
- (NEW!) Supports Substances in 2017 and 2018+,
- (NEW!) Supports Meshes with UVs out of bounds (Outside of [0, 1] UV space) for both Mesh and Material Merger.
- (NEW!) Added support for Amplify Impostors and ability to automatically generate Impostors for specific LODs.
- (NEW!) Material Merge outside of the Merger Tool and use/share the baked data in any Merger Component, saving iteration time, reducing combined textures and draw calls;
- (NEW!) Merge groups of objects using a grid (Great for large modular zones);
- (NEW!) Use custom objects for specific LODs instead of using the merger (Imposters, custom mesh, etc);
- (NEW!) - Ability to include custom components by duplicating the original raw collection and removing not needed components.
- Merge groups of objects with the same materials into one single object;
- Merge groups of objects with different materials into a single object with a single material;
- Non-destructive workflow (easily go back and forth between the original and merged objects, for a single or multiple Merger groups in the scene)
- LOD Generation with control over percentage of meshes and minimum size per object per LOD;
- Include/exclude specific materials from LODs;
- Material merge specific groups of objects with specific materials into their own merged object (e.g. Separate objects for Standard Opaque and Standard Cut-Off);
- Share merged materials between different LODs;
- Easy and powerful texture and material setup for Material Merger with scriptable objects;
- Re-use already baked lightmaps used by the original objects for the new merged objects;
- Re-position UV2 Lightmap UVs so they do not overlap (for use with baked lightmaps);
- No coding required when using in the Editor;
- Run-time support;
- Generate cloned colliders from original objects;
- Perform Merger to every Merger group in the scene with one click;
- Switch between the originals and merged objects of all Merger groups in the scene with one click;
- Prefab creation and save all merged meshes/materials/textures inside a given project folder;
- Preview merged statistic results before performing merge generation.
- Full source code.

Supports:
- Skinned Meshes;
- GameObjects with or without LODGroup component (Will use original object's LODs for the merged LODs);
- Tiled/Offset/Scaled Materials;
- Multiple Materials per object;
- Meshes with UVs out of bounds for both Mesh and Material Merger.
- Substances (Editor only, not at run-time );
- Color multipliers in materials can be applied to textures in merged materials;
- Unity 2017/2018 (Tested all version from 2017.1 to 2018.2);
- Default Renderer, HDRP and LWRP;
- Any Shader. Keywords can be enabled when using Material Merger.

Results:
- Massive draw call reduction;
- Reduced number of shadow casters;
- Improved performance on both the CPU and GPU;
- Improved realtime lightmap results (especially for modular scenes);
- LODs are treated for the group as a whole instead of per object;
- Easy to work with and to change objects even after merging them.
- Slightly higher memory usage due to extra meshes and textures;

Current Limitations (Will be resolved in updates):
- No Run-time Substance support (Works just in editor);

Roadmap:
- Run-time Substance support.

Possible features for future versions:
- Automatic Mesh polycount reduction;
- Add objects to already merged objects efficiently at run-time;

Visit the official thread on the Unity forums for more information/questions/feedback/requests: Advanced Merger Toolkit Thread