To solve this question, the user needs to know the rules of comparative and superlative forms of adjectives. The correct sentence should use the superlative form of the adjective “fancy” to indicate the highest degree of fanciness.

Now, let's go through each option and explain why it is right or wrong:

A. fancyest: This option is incorrect because it uses an incorrect form of the adjective "fancy." The correct form of the superlative degree of "fancy" is "fanciest."

B. fanciest: This option is correct. The superlative form of "fancy" is "fanciest." Therefore, this sentence uses the correct form of the adjective.

C. most fanciest: This option is incorrect because it uses both the superlative "most" and "fanciest" together, which creates redundancy. Using "most" and "fanciest" together is unnecessary and incorrect.

D. fancier: This option is incorrect because it uses the comparative form of "fancy," which indicates a comparison between two things. The sentence requires the superlative form of "fancy" to indicate the highest degree of fanciness.

The Answer is: B. fanciest