Sort of an inbetween one (regular in the endings at least, like everything), declines like its root: "nieść"
"With nieść and móc, the o of the stem becomes ó in the third-person singular masculine. With nieść, the o of the stem becomes e in the masculine personal plural."
Swan, Oscar (2008-10-12). Polish Verbs & Essentials of Grammar, Second Edition (Verbs and Essentials of Grammar Series) (Kindle Locations 1354-1357). McGraw-Hill Education. Kindle Edition.