How many times have you wanted to study monsters or perhaps have had a PC ask you for a related skill? Here's an alternative to give players allowing them to know things about particular monsters that they otherwise shouldn't know.
Knowledge (Int; Trained Only)
Charaters must select a group of enemies that they are knowledgable about. Use the favored enemies table (PHB pg. 45) as the list of enemy types. The character has then studied and obtained a level of knowledge on those particular creatures. This knowledge can include specific weaknesses of the creature, such as using fire or acid versus a troll.
Check: For simple resolution, any creature of a CR of equal or lesser value to the character's knowledge skill is known by the character. For randomization this check can be (10 + CR of creature) and the character performs a normal skill roll.
Retry: Yes, but only after the character has increased the ranks in this skill.
(Note: although this gives the character information about the creature, it does not give them the skill and attack bonuses that a ranger gets.)
Knowledge (Int; Trained Only)
Charaters must select a group of enemies that they are knowledgable about. Use the favored enemies table (PHB pg. 45) as the list of enemy types. The character has then studied and obtained a level of knowledge on those particular creatures. This knowledge can include specific weaknesses of the creature, such as using fire or acid versus a troll.
Check: For simple resolution, any creature of a CR of equal or lesser value to the character's knowledge skill is known by the character. For randomization this check can be (10 + CR of creature) and the character performs a normal skill roll.
Retry: Yes, but only after the character has increased the ranks in this skill.
(Note: although this gives the character information about the creature, it does not give them the skill and attack bonuses that a ranger gets.)