Combine and modify meshes:

// Merge multiple meshes into one for better performance
const merged = BABYLON.Mesh.MergeMeshes(
    [box, sphere, cylinder],  // Meshes to merge
    true,                     // Dispose original meshes
    true,                     // Allow different materials
    undefined,                // Use default world matrix
    false,                    // Don't clone meshes
    true                      // Allow different vertex colors
);

// Create instances for repeated objects with shared geometry
const boxInstance = box.createInstance("boxInstance");
boxInstance.position.x = 5;

// Create many instances efficiently
for (let i = 0; i < 100; i++) {
    const instance = box.createInstance("box" + i);
    instance.position = new BABYLON.Vector3(
        Math.random() * 20 - 10,
        Math.random() * 5,
        Math.random() * 20 - 10
    );
    instance.rotation.y = Math.random() * Math.PI * 2;
}