There are different enemies that roam around the lands of Eos. Each of them have strengths and weaknesses that are exploitable. Many of these creatures also may only appear when certain requirements are met. Some of these creatures are also farm-able. People can get some items from them to boost their spell power. Other times, these creatures have elements that can used in Elemancy. When trying to extract elements from them, use either the Valiant, the Engine Blade, or any weapon that increases the rate of absorption. Also, the Ascension path has the Element Magnetism which increases the chances of dropping elements when trying to farm for it.
Most Beasts can be found anytime but preferably to fight them in the morning. They often drop a variety of items that can help in coming up with new recipes or even help you boost your spells. Some creatures spawn only when you take in a quest or may be part of the main storyline. Each creature has its specific drop and weaknesses in order to defeat it.