Many Adventurers throw the term 'Monster' around with ease, especially when talking about their past exploits to their peers, however the truth regarding Monsters in and around Thistleland is more complex then simply applying emotion to a word.
The Adventure Guild currently holds the widely accepted classification of Monsters, and considers a Monster as "Any creature that understands and accepts a change in their behaviour that will both benefit themselves and reduces harm to another creature, then deliberately and wilfully chooses not to enact said change to their behaviour".
In laymen's terms, this mean any creature that will not change it's methods to the benefit of itself and others. This type of wording has made it clear that in The Guilds mind that sentient creatures, people, can be considered just as much Monsters as some mindless husk. Indeed, there are many documented cases of people who have specialised abilities being classified as Monsters due to how they use these abilities, and even otherwise normal people who allow themselves to be consumed by desires of revenge.
On the other side of the argument while many creatures in Thistleland may be called monstrous, such as the Marrow Mosquito, they are still not officially Monsters. An aspect of understanding on the part of the creature must be confirmed for The Guild to state that a creature is officially a Monster.
Due to the above, Monsters are relatively uncommon in Thistleland and surrounding continents, but they do indeed exist. Individual people that are Monsters may be treated with due to their complex nature, though The Guild advises against this and therefore you are to do so at your own risk.