jgsugden
Legend
Each creature type has a core concept. They pick the creature type by looking at which core concept is closest to the description of the monster they have created/revised.
There are some monsters that can go either way. Fomorians are giants that have had their ineage subjected to a few curse. They could have been fey, or giants. However, the designers felt like they were still more closely tied to the concept of a giant than to a fey creature, so the selected giant. The new Liondrake/Dragonne is a mix of lion and dragon. It could have been a dragon or a monstrosity. They elected to go with monstrosity because it had more in common with creatures like manticores than it did with a true dragon.
In other words - it isn't a science - it is a subjective art.
There are some monsters that can go either way. Fomorians are giants that have had their ineage subjected to a few curse. They could have been fey, or giants. However, the designers felt like they were still more closely tied to the concept of a giant than to a fey creature, so the selected giant. The new Liondrake/Dragonne is a mix of lion and dragon. It could have been a dragon or a monstrosity. They elected to go with monstrosity because it had more in common with creatures like manticores than it did with a true dragon.
In other words - it isn't a science - it is a subjective art.