Action verbs:
* Splat: "The mud splattered on his shoes."
* Squish: "He squished his feet through the mud."
* Trample: "The hikers trampled the muddy path."
* Wallow: "The pigs wallowed in the mud."
* Dredge: "They dredged the mud from the river bottom."
* Smear: "The child smeared mud all over his face."
* Throw: "She threw a handful of mud at her brother."
State of being verbs:
* Be: "The ground was covered in mud."
* Become: "The once-paved road became muddy after the rain."
* Stay: "The mud stayed on his boots long after he left the field."
Other verbs:
* Clean: "She cleaned the mud off her shoes."
* Remove: "He tried to remove the mud from his clothes."
* Dry: "The mud dried in the sun."
* Solidify: "The mud solidified into a hard crust."
To give you a more specific answer, tell me what kind of action or state of being you're thinking of!