So I mirrored my mesh then tried to combine it to another mesh then this happened Before combining them together it looks fine after combining them it turns wired and shit
Do you mean weird? That's the normals flipping for what ever reason, go to edit mode, select all and recalculate normals (was it ctrl+n?).
you can also go to a tab on the left (i believe shading or uvs or something) where theres a button to recalculate normals