Question

They are all fictional heroes.................. adventures are filled with unbelievable danger (who-which - whose - what)​

Answer 1

They are all fictional heroes.........whose......... adventures are filled with unbelievable danger (who-which - whose - what)

Answer 2

The correct relative pronoun to use in this sentence is "whose."

"They are all fictional heroes whose adventures are filled with unbelievable danger."

The word "whose" is used to indicate possession or ownership, in this case, the adventures belong to the fictional heroes.