OK, so you have a big book of monsters - in this case Bestiary 4 for the Pathfinder RPG - but what are you going to do with them?
If you want more than just plonking a monster in front of the party for them to fight, but do not have time to figure out full-blown encounters, have a look in here. There are twenty monster-driven encounters here, some are just about a mini-adventure with a single monster antagonist, others are just something the party may come across when they are doing something else entirely. All draw on the particular focus of Bestiary 4, the creepy nightmarish things that develop from evil events or which crawl in from other planes.
For each monster, there's some descriptive text that may be what the characters come across or perhaps it provides some background. There are notes about what is going on and how you can involve the party; and there are several variants of the encounter so you can pick the one which suits the rest of your campaign best (or. of course, the version that takes your fancy!). Whilst you'll need a copy of Bestiary 4 for full effect, critter stat blocks are provided here, although the full details of the creature in question will be found in the pages of the Bestiary.
To make it even more useful, there is a set of separate 'character sheets' for every creature that you'll encounter in these pages as well as all the relevant Hero Lab data files if you use that system. There are three versions of the main document too, as well as the usual full version and a printer-friendly one, there is one with all the stats omitted just giving you a collection of encounters.
The encounters are inventive, many are capable of being developed into a short adventure in their own right or of being woven into an ongoing plotline should you have time and inclination. Otherwise, you can just have them pop up 'as is' whenever you feel things are getting dull!