Skeleton

A skeleton on the party's side is unusual but well-supported in the SRD: an Animate Dead caster in the party, a friendly necromancer NPC who has loaned out a unit, or a temple of a death-domain god where skeletons serve as silent attendants. The framing that lands at most tables is the wizard's first Animate Dead cast: two skeletons, given a one-line standing order, following the party for the next 24 hours.

Use them as front-line bodies. AC 14, 13 HP, +5 melee at 1d6+3, +5 ranged at 1d6+3 to 80 ft.; that is an extra body in the line at zero cost beyond a 3rd-level slot. A two-skeleton screen lets the wizard cast at the back without taking a club to the face on round one. Issue clear orders before initiative: "Engage anything that crosses the doorway," "Shoot the goblin in the green hood until it falls," "Stand here and do not move." Skeletons follow the letter, not the spirit.

What they cannot do: open complicated locks, hold a coherent conversation, distinguish friend from foe in a melee, or recognize a polymorphed ally. They are immune to Poison damage and to Exhaustion and Poisoned conditions, so they tank traps the party would otherwise eat. They are also Vulnerable to Bludgeoning, so an enemy with a maul will end them in one turn. Position accordingly.

The party is responsible for retiring them. A skeleton that runs out of orders stands still until destroyed or commanded again. Burial, dismantling, and the appropriate prayers are the cost of using the dead, and most settlements will demand them.

Have one of the skeletons keep its old armor and a wedding ring on its finger. The party should remember that this thing was a person.

A skeleton is the cheapest way to teach a level-1 party that AC 14 still matters. CR 1/4, 13 HP, +5 to-hit with both shortsword and shortbow for 6 average damage, and a Dex of 16 that wins most initiative rolls. Run them in groups of four to eight; one skeleton is a warmup, four is a real fight, and eight is a wall of bone with a longbow line behind it.

Open at range. Skeletons are ambush units in their own crypts. Bowmen on a balcony, in a stairwell, or behind sarcophagus lids open with shortbow shots from 80 ft. while a melee rank waits in the doorway. The +5 to-hit is real against AC 13 and 14 targets, and 6 piercing per arrow stacks fast across a four-skeleton volley. When the party closes, the front rank steps up with shortswords and the bowmen drop their bows for melee. They do not flee or surrender. They just keep cutting until something puts them down.

Damage type is the puzzle. Bludgeoning is a Vulnerability, so the cleric's mace, the warhammer fighter, and a bag of caltrops dropped from above all deal double dice. Poison is immune, Exhaustion and Poisoned conditions land for nothing. Spells like Sleep, Charm Person, Cause Fear, and Hold Person are immune-by-creature-type or save-immune in practice, since most fear-and-charm spells require a Humanoid target. Lean the encounter on damage and on the cleric's Turn Undead if the party has one.

These are puppets, not soldiers. They obey a standing order from the necromancer who raised them and they do not adapt mid-fight. If the party flanks the bowmen, the bowmen still aim at whatever target the order specified. That predictability is the gift to a clever party. Reward it.

Have the skeletons act in unison. All four loose arrows on the same count, all four step forward on the same beat. When the party first hears the rattle of bone moving in lockstep, that is the encounter.