Skeleton

The Skeleton is a lesson in picking the right weapon

How to run it. 13 Hit Points, AC 14, Initiative +3, a Shortsword and a Shortbow both at +5 for 1d6 + 3. Against a party member in AC 16 the bow hits half the time. Skeletons are the cheapest undead that can shoot, so put them behind something: a rubble wall, a balcony, the far side of a pit.

The rule that matters. Vulnerability to Bludgeoning damage. Bludgeoning hits deal double. A longsword (1d8 + 3) can never drop a fresh skeleton in one hit; its best roll is 11. A warhammer with the same +3 does 2 × (1d8 + 3) and one-shots it 62.5% of the time. Even a mace (1d6 + 3) does it 50% of the time. The same fighter, same Strength, different tool.

It is also immune to Poison and to the Exhaustion and Poisoned conditions, so the rogue's poisoned blade and the gas trap do nothing.

The common mistake is hiding the weakness in the stat block. Show it: the arrow slides between ribs and clatters out the back, the club shatters a skull. Players who hear that difference switch weapons by the second round.

For players. Carry a cheap bludgeoning weapon, even if it is not your main one. A light hammer or a club costs almost nothing and turns a two-hit fight into a one-hit fight. The Shatter spell does Thunder, not Bludgeoning, so it gets no double.

Lore from the rules. The 2024 stat block says a skeleton understands one language besides Common but cannot speak. It hears your threats and your plans.

The human angle. In 1942 Abraham Luchins gave people water-jar puzzles that all shared one long solution, then a puzzle with a short one. Most kept using the long method. He called it the Einstellung effect: a method that has worked blinds you to a better one. A player who has swung a sword for six sessions will keep swinging it at bones.

Source: Luchins, A. S. (1942). Mechanization in problem solving: The effect of Einstellung. Psychological Monographs, 54(6), i–95. doi:10.1037/h0093502