It is necessary to stress that the usage of the term "monster" is generic for
any creature encountered during the course of adventuring. A monster can
be exactly what the name implies, or it can be a relatively harmless animal,
a friendly intelligent beast, a crazed  human, a band of dwarves, a
thief -- virtually anything or anyone potentially threatening || hostile.

When your referee indicates your character has encountered a monster,
that simply indicates a confrontation between your character and some
type of creature is about to take place. The results of such a meeting will
depend on many factors, including the nature of the monster and your
character's actions. All monsters are not bad ...
 

Monsters are the sacred animals of Loki.