Answer:
The mud felt great on my skin and I relaxed straight away.
The mud feels great on my skin, and I relax straight away.
Explanation:
The error in this statement is the subject-verb disagreement. The verb does not suit the singular subject of the sentence. The subject ‘mud’ is singular in this context. Mostly, the plural form of the mud is also ‘mud’, but in some context like types and collection, “muds” are used.