Monsters, also known as Mobs, are enemies that Maplers will encounter throughout their journey in MapleStory. They drop Mesos and various items upon elimination, and is one of the main way where Maplers gain experience points (EXP) from. Many quests require players to eliminate monsters and/or acquire items from them.
Depending on the monsters' level, their behaviour can vary from being disarming to those which attack upon sight.
When hurt, or cast with a debuff, low-level and weak monsters will simply follow the player to damage them using physical contact, whereas some higher level monsters, along with Boss Monsters, will not only follow but retaliate with ranged, magical attacks, debuffs (e.g. slowing, disabling attacks, using of items and other abilities) and benefitial buffs on themselves as well (e.g. increased defense or attack), which can serve more dangers for them. Even higher level mobs will attack or activate their buffs when a player gets anywhere nearby them.
Low-level monsters are mostly found in tutorial areas (i.e. Maple Island, Ereve, Rien and etc.), of which they appear to be adorable and friendly. Higher level monsters can be seen in many areas, but are usually restricted in dungeons or are found in the Ossyrian regions where monster levels are generally higher. Boss Monsters on the other hand, appear in specific maps of which they will only spawn in. High level Boss Monsters often shown on the Boss Tab in the Party Window have a limit of times they can be faced in a certain period of time that increases they higher the level is.