A bestiary is a list of the monsters in an area or in this case a game. This bestiary is about the monsters in Old School RuneScape.
Below are links to bestiary lists organised by the monster's levels:
Free-to-play has their own bestiary without pay-to-play monsters:
Navbox JSON: {"groups":[{"contents":[{"text":"Free-to-play","link":"Bestiary/Free-to-play"},{"text":"1-10","link":"Bestiary/Levels 1 to 10"},{"text":"11-20","link":"Bestiary/Levels 11 to 20"},{"text":"21-30","link":"Bestiary/Levels 21 to 30"},{"text":"31-40","link":"Bestiary/Levels 31 to 40"},{"text":"41-50","link":"Bestiary/Levels 41 to 50"},{"text":"51-60","link":"Bestiary/Levels 51 to 60"},{"text":"61-70","link":"Bestiary/Levels 61 to 70"},{"text":"71-80","link":"Bestiary/Levels 71 to 80"},{"text":"81-90","link":"Bestiary/Levels 81 to 90"},{"text":"91-100","link":"Bestiary/Levels 91 to 100"},{"text":">100","link":"Bestiary/Levels higher than 100"}]}],"name":"Bestiary","title":"[[Bestiary]]"}