If you would like to unlock Monk bestiary I recommend to choose:
Dark Cathedral floor- 2 along with bestiary for Witch (15), Ghost (15), Dark Apprentice (15), Dark Monk (15), Assassain (15) and many more.
More details about Dark Cathedral:
Introducing the ability to bump and pin questionsJanuary 09, 2022
Fourth Anniversary InfographicDecember 30, 2021
Interview with Laethye - Game Content Designer of TibiaNovember 23, 2021