Myoblast-specific protein that mediates myoblast fusion, an essential step for the formation of multi-nucleated muscle fibers (PubMed:28569745). Involved in membrane fusion downstream of the lipid mixing step mediated by MYMK (By similarity). Acts by generating membrane stresses via its extracellular C-terminus, leading to drive fusion pore formation. Acts independently of MYMK (By similarity). Involved in skeletal muscle regeneration in response to injury by mediating the fusion of satellite cells, a population of muscle stem cells, with injured myofibers (By similarity). Interacts with MYMK. The AxLyCxL motif is required for myoblast fusion. Belongs to the MYMX family.