Goat

A goat is a pack animal, a druid's wild shape, or a pastoral cult's holy companion. Most common: someone bought one in the last village to carry gear and give milk. The party named it. Now it's permanent.

Don't field it in combat. AC 10 and 4 HP means one arrow kills it. Keep it tied at camp, behind a real fighter in the marching order. If a player insists on using it, it charges at 40 feet, headbutts for whatever improvised damage the GM rules, and dies. Stop this from happening by accident.

The goat's value is outside combat. Climb speed 30 feet reaches ledges the rogue can't. A rope around its body solves traversal problems. Darkvision 60 feet and Passive Perception 12 mean it notices the wolf at the treeline before watch does and bleats. A goat bleating at 3 a.m. saves more parties than initiative.

Have the goat eat a plot-relevant note in the second session. The party will laugh, then spend an hour digging through dung to recover what was written.

A goat is CR 0 with 4 HP, AC 10, and a Ram attack at +2 for 1 bludgeoning (or 1d4 if it charged). It's not a fight; it's a complication. If the party swings on it, it dies on the first hit and nobody feels good about it.

Use the goat as terrain. Walk speed 40 feet, climb speed 30 feet means the goat is faster than armored PCs and can reach ledges the party can't. Passive Perception 12 and Darkvision 60 feet mean it sees the party in any light. A mountain herd above the road isn't aggressive on purpose, but a goat dislodging a rock down scree onto the party is a Dex save, not combat. Let the terrain do the work.

Or use a herd. One goat is a punchline. Twenty stampeding through a market while the party chases a thief is a skill challenge. Athletics to vault stalls, Animal Handling to part the herd, Acrobatics to keep balance when a billy blocks your shins. The table doesn't want to-hit rolls on goats.

If a player insists on attacking one, let them kill it in one hit. Then the herder arrives with a bill and an opinion. The financial consequence is more interesting than the combat round.