In God's Domain, monsters are entities that are neither NPCs or players. They are hunted by players in order to gain Exp and Loot.
Every monster in God's Domain has their ranks, species and some are even given titles.
In God's Domain, aside from special cases, most monsters would only start developing high intelligence after reaching Tier 3. In other words, this was a concern after monsters became Great Lords. At that stage, monsters would be more difficult to deal with. They would often act in unexpected ways. Situations such as monsters ignoring MTs and going for the rear line healers occurred when one dealt with monsters at this rank. In these situations, the MTs combat experience would be put to the test. Not only must MTs attract the Bosses' aggro, but they must also hold the Bosses' attention. As for DPS classes, they had to do the opposite. When attacking, they had to make sure they attracted as little attention as possible.
Past Level 100, monsters at the Grand Lord rank and above will become immune to the effects of Basic Barrier-type magic arrays. Players would have to resort to using Intermediate Barrier-type Magic Arrays and better to suppress these monsters. 
Monsters have differing combat standards. As players encounter higher levels and higher rank, monsters would start exhibiting higher combat standards.
One of the factors that affect the monster's combat standard is the number of HP bars they have. An additional HP bar would signify a higher level of combat standards as compared to a monster with only one HP bar. A monster with three HP bars could exhibit combat standards on par with players who could reach the Trial Tower's third-floor, while a monster with five HP bars could reach the Trial Tower's fifth-floor. Although this evaluation method was not necessarily accurate, it was not that far off the actual numbers.
One of the factors that affect the monster's combat standard: their weapons. For example, monsters that use a two-handed axe would rely on simple combat methods and rely on great destructive power. In comparison who uses a trident or spear, which has a longer attack range and allows for more flexibility in their attack patterns. 
Similarly to players, monsters are able to reach higher tiers, via evolution.
Whenever a Field Boss is killed, the map it was in becomes ruler less. In such a situation, the monsters in the map would engage in an intense battle, that stimulates their growth, allowing them to evolve into a strong being. Hence, every time a new Boss appears in a region, the region's monsters would grow more powerful due to their evolution during the intense competition.
Any method of evolution is via Bloodline Evolution. For some Demonic Beasts, they are members of powerful bloodlines that were passed down since the ancient era. However, due to the reduced potency of the bloodline, this monsters do not possess the same powers as their orginator. There is a possibility to triggering their bloodline when the monster is evolving, which would allow the monster to improve their Tier and improve their Life Rating.
Monster ranks can be broken into the following: Common, Elite, Special Elite, Chieftain, High Chieftain, Lord, Rare Lord, High Lord, Great Lord, Grand Lord, Mythic, High Mythic, Superior Mythic, and God
Rare monsters have are equal in combat power but drop better loot.
Chieftain ranked monsters are stronger than those of a lesser rank due to possessing unique traits. This traits can be special buff skills, skills with extraordinary destruction capabilities, skills with a super long range and so on.  Rare Lords are more powerful than ordinary Lords due to having an additional innate skill. 
There are special ranks that are given to sea-based monsters: King-class
Among monsters, each of them would belong to a certain species. Each of these species would have their own abilities and enhanced combat standards
- Elemental Being
- Ferocious Beast
- Special Lifeform
- Archaic Species
- Inferior Dragon
- Marine King Creature
- Sea Monster
- King-class Sea Monster
- God - born naturally
- God - ascended to Godhood
- Dark Creature
- Demonic Beast
- Humanoid Creature
- Mechanical Lifeform
- High Human
- High Demon
- High Inferior Dragon
- Realm Lord - Realms Lords have stronger Skills, Spells, and physique, compared to Mythic creatures of the same level. 
- Field Boss - Normal Grand Lord Field Bosses have around 3 to 5 HP bars, while Mythic Field Bosses have 5 to 7 bars. 
- World Boss - Normal World Bosses have eight or more HP Bars
- Tier Master - Creatures who have superior combat standards, and able to summon monsters if the total number of participants exceeds a certain number. Summoned creatures are equal to experts at the third floor standard of the Trial Tower. 
- Bloodline Creatures 
- Thunder God's Kin 
- Monarch Bosses - Monarch Bosses are Superior Mythic creatures and wield more power than Mythic ranked Archaic Species