"Puzzle at the End of the Book" is a very challenging puzzle from the 2017 MIT mystery hunt. The answer of this puzzle is a 6-letter word, related to woman's beauty. The solution is intricate, and requires careful analysis of the book, some geeky references, and possibly lots of Google searching as well.
The answer to this puzzle is MAKEUP.
In order to get to it, first you must find 6 secret fantasy related words.
1. The green words on the pages of the book form the sentence Wooden ship turned around before understanding sea monster (SIX). "Wooden ship" = ARK, "turned around" -> KRA, "understanding" = KEN, so we get KRAKEN, which is a sea monster with six letters.
2. The broken lines along the speech bubbles can be decoded using morse code to spell Lilith, Morrigan, Scarlet, or Queen of Pain. These female demons give the secret word SUCCUBUS.
3. The ship, the brick wall, the ladder, and the bucket contain four hidden brail letters, which spell out the word HUMA.
4. Grover's arms encode through semaphore the Inuit mythological creature QALUPALIK.
5. The word "Puzzle" is written in five different fonts - Times New Roman, Impact, Twentieth Century, Arial, Nosifer. The first letters of these fonts form the word TITAN.
6. Each page from 2 to 8 contains some unusual words. Part of these words, combined with immedietely preceeding/succeeding parts of neighboring ones, give the six Pokemons Sandshrew, Pinsir, Ekans, Clefairy, Tentacruel, Eevee, Rapidash. Their first letters form the secret word SPECTER.
The names of the six muppets on the last page are Barkley, Donmusic, Elmo, Kermit, Misspigy, Oscar. They perfectly match in terms of length with the six secret words which we found above. Also, each pair of name with secret word overlap in just one position, the six resulting letters are E, U, M, K, P, A. If we arrange these letters with respect to the length of their correspnding words, we get the final answer MAKEUP.