Sometimes, you will face enemies that appear to be invulnerable to your attacks, due to their damage reduction or regeneration. The latter is particularly bothersome if you don’t have the right weapon or spell on hand.
Playing dungeons and dragons alone means you will have access to the stat blocks of every creature, including all it’s weaknesses. The trouble is, unless your characters have been told by an NPC what a monster’s weaknesses are, they shouldn’t have this information.
A spell such as Lore of the Gods might allow a character to know what the weakness of a creature is, but when such a spell is not available (i.e. you don’t have the book), you need to find other ways of discovering a monster’s weakness(es).
If you come across a monster that won’t stay down no matter how hard you beat it, resist temptation to meta-game and try the following instead:
The spot skill can be useful in picking up visual clues regarding a creature’s weakness. A troll that is only harmed by fire might have burn scars on it’s body, hinting that injuries caused by fire won’t heal instantly like other injuries do.
In this case, your character(s) could make a spot check with a DC of 15-25, depending on how well hidden/old the scar is. The character must be actively looking for any tell tale signs of the monster’s weakness.
Once a character spots the clue, have him or her make a wisdom check of DC 10-15 (or higher). Succeeding on the check means he or she has identified the weaknesses. A failure by 4 or less means the character is no wiser and a failure by 5 means he/she mistakes the source of injury for something else (e.g. lightning instead of fire).
Monsters such as trolls are fearless, simply because they cannot be killed – except by fire or acid. So when a paladin suddenly whips out a flaming sword, it’s only natural to assume that the troll would at least react in some minor fashion. For instance, they might hesitate/flinch for a moment mid-charge before pressing ahead with their attack.
In order for a character to pick up these tell tale signs of fear or uncertainty, you can have them make a sense motive or wisdom check. The DC can be set at 10-20 depending on how subtle or extreme their reaction is. For extremely powerful creatures or creatures immune to fear, the DC could be even higher at 25 or 30.
Experienced adventurers are often knowledgeable about one or more aspects of their profession, including creatures related to their field of expertise. The various knowledge skills represent this knowledge which is often gained by reading books/scrolls or professional experience.
Certain books such as the Monster Manual IV onwards and the Fiendish Codex I give good knowledge DCs for each creature that is listed in the book, so if you are unsure about setting the DCs yourself, refer to these books as a guideline.
As a general rule, the knowledge check DC required to recall information about a monster is equal to 10 + the hit dice of the monster. Refer to the knowledge skill descriptions in order to find out which creature types are covered by each knowledge sub skill.
If all else fails, try everything and pray something works.
Probably the most obvious thing to do if you find you’re beating a monster that simply won’t stay down (or even feel pain at all). Use every weapon, try different spells and break out all those consumable magic items you probably never use.
To avoid meta-gaming, add a bit of randomness to the selection of tools by rolling a die. E.g., you are carrying three weapons, so you assign a number from 1-3 for each weapon and roll a 1d4, ignoring rolls of 4.
Retreat! Let’s Ask the Townspeople!
Only a fool would continue to beat on a monster when its clear he simply cannot kill the monster with the tools currently at his disposal. As long as circumstances permit, you could retreat and head back to town.
Once there, perform a gather information skill check, representing your asking around for someone who might know more about the beast. To ask about the creature itself, you could make a gather information check with a DC equal to 10 + monster’s challenge rating.
If the gather information DC is 20 or higher, then the information is only available from knowledgeable experts and sages.
Used in this fashion, retreat can be a valid way of learning a creature’s weakness. Just make sure you’re not travelling with a paladin when calling for retreat…
These are just a few ways you can discover the weaknesses of a monster without meta-gaming when playing alone. As you begin to build this knowledge, you might want to record them on Word for future reference in case you come up against the same kind of monster again. If you have something to add to this list, please feel free to do so on the comments box below.