As a Roblox developer it is currently impossible to mirror (inverse/flip) a MeshPart in Roblox.
Other game engines usually solves this by allowing the property Scale / Size to become negative values, while it is capped to minimum 0.05 in Roblox.
Concrete example where this is a problem is when you build a modular pet system (could also be vehicles) and you want to reuse a part for both the left and right side. The optimal case here would be to create a mesh part for the left side part, then attach it mirrored using a script on the right side.
I would like to see this as well. I was running into this problem yesterday, and the only work-around is if you convert your MeshPart to a SpecialMesh and negate the x scale. The problem is you will only be able to get the sizing to match if you know the original size of your MeshPart before any scaling is applied. There’s no way AFAIK to obtain the original size of a MeshPart programatically, but if you do know it you could do something like:
I think a mirror property would be very useful, and it seems doable considering MeshPart.DoubleSided was added. Mirroring would be across the X axis and apply to physics data too. I’m working on adding realistic structures using uploaded meshes, and it would really improve variety and modularity to be able to mirror a complex mesh without needing to upload a second mesh with completely separate physics data.