The word "superlative" can be a noun, adjective, or adverb depending on how it is used in a sentence.
superlative adjective
adjective (superlative form)
Costliest is an adjective. It is the superlative of costly.
"toughest" is an adjective ( the superlative form of "tough" )
The word "hardest" is an adjective, as it describes the superlative form of the adjective "hard."
an adjective (the Superlative).
it is superlative
"Craziest" is an adjective in its superlative form.
superlative adjective
Greatest is the superlative adjective of great.
adjective (superlative form)
An adjective in its superlative form.
Darker is a comparative adjective
Scariest is the superlative form of the adjective scary.
Largest is an adjective. It's the superlative form of large.
Biggest is an adjective. It's the superlative form of big.
Fluffiest is an adjective. It's the superlative form of fluffy.