Possessives show possession or belonging, and are formed with the addition of an apostrophe + s to the end of a noun.
Things we can see, touch, feel and count are concrete nouns. Abstract nouns name nonphysical ideas, emotions, states and qualities, like empathy, justice and buddhism.
Not all heroes wear capes, and yes, ‘heroes’ is the correct plural of hero.
Cliff plural is cliffs. Usually singular nouns that end in -f/-fe take on -ves as a plural. This is not the case with cliff/cliffs.
Volcanoes and volcanos are both accepted plurals for volcano.
The plural of concerto is concerti and concertos.
Zeroes or zeros are both accepted plurals of the noun (and non-figure) zero.
The plural of codex is codexes and codices. Codex comes from the Latin, and uses Latin suffixes.
Both dogmas and dogmata are accepted plurals of dogma (sing. n.). Dogmata is the original Greek pl. n. form; dogmas is the Americanized plural.
Errata is the plural form of erratum.