Multi-spin galaxies present spectacular evidence of the galaxy formation via merging or accretion of the baryon matter with different orbital angular momentum orientation. This term combines both counter-rotated and polar ring/disc systems. I discuss what long-slit and 3D spectroscopy tells us about the coexistence and interaction of mutli-spin gaseous subsystems in galaxies. The impact of shock waves in gas ionization in host discs and polar structures is considered. In some cases, a close relation between the properties of gas ionization and its line-of-sight kinematics (peaks of velocity dispersion or double-component emission lines) is observed.