muddy up vs muddy

muddy up is not an adjective while muddy is an adjective.

Word	Noun	Adjective	Verb	Adverb
muddy up	No	No	Yes	No
muddy	No	Yes	Yes	No

As verbs, muddy up and muddy are synonyms defined as:

muddy up (adjective)	muddy (adjective)
	dirty and messy; covered with mud or muck
	(of color) discolored by impurities; not bright and clear
	(of liquids) clouded as with sediment
	(of soil) soft and watery