Did you let it hold the item? I can't remember the name but it just prevents that Pokemon that holds that item from evolving.
Marshtomp evolves into Swampert starting at level 36.
at level 36
Mudkip evolves into a Marshtomp at level 16.
Marshtomp can evolve at level 36.36 lv.
it doesnt
...evolve? Marshtomp evolves at level 36 into Swampert.
Marshtomp evolves at Level 36.
Mudkips only evolve by leveling up. At level 16 a mudkip will evolve into a marshtomp and at level 36 the marshtomp will evolve into a swampert.
level 36
Swampert can't be found in the wild. You have choose Mudkip as your starter Pokemon, and evolve it into Marshtomp (at level 16), then into Swampert (at level 36).
yes
it doesnt evolve in any generation so far hope i helped. by night