Muksia means to beat up someone, but it is meant in playful way and not seriously. At least in my dialect it does. Muksia comes from "mukiloida", which means the same thing but isn't playful. I don't know if some other dialects have different meaning for it.

These kind of sentences you can find in any local Finnish newspapers: Kaverukset Janne ja Pekka särpivät alkoholituotteita ja jostain syystä riitakin saatiin aikaan. Lopulta miehet muksivat toisiaan nyrkein ja pientä painiakin käytiin.