http://www.math.ohio-state.edu/~econrad/lang/ln1.html

Case Singular Plural Rough translation

Nominative matella matellae the chamber pot(s)

Genitive matellae matellarum of the chamber pot(s)

Dative matellae matellis to the chamber pot(s)

Accusative matellam matellas the chamber pot(s)

Ablative matella matellis by means of the chamber pot(s)

Locative matellae matellis at/in the chamber pot(s) (obsolete)

Vocative matella matellae O Chamber Pot(s)! (rare)

(“Vis” is an entirely different noun that means “power or strength”).