Giant Boar

A giant boar as ally is almost always a druid's wild shape, a ranger's beast companion variant, or the party earning a debt because they killed the poacher who caged it. Less commonly, an orcish or halfling cavalry tradition uses giant boars as mounts, and the party has been gifted one for a war season.

Run it as a heavy charger with no plan. The boar moves 40 ft., slams into the target the rider points at, and keeps slamming until told to stop or the target falls. A mounted PC gets a stable platform with Str 17, which is excellent for trampling formations of light infantry but terrible for skirmishing in tight quarters. The boar won't back through doors smaller than a barn. It's Large, so it eats two squares of any indoor map.

The boar offers nothing else. It cannot scout, carry messages, or distinguish between friendly and hostile humanoids beyond what its handler signals. If the handler is downed mid-fight, it defends the body and attacks anyone who approaches, including allies. Plan for that. Out of combat, it eats three rations a day, smells like a swamp, and any innkeeper takes one look and quotes triple the stable fee.

Give the boar a name and a single quirk. The party will love it more than the horse they paid for, and they will mourn it harder when it dies.

A giant boar is a furious freight train with tusks, and it works best as a wilderness encounter the party didn't pick. It's a beast, Int 2, and it doesn't ambush so much as it gets surprised in its own clearing and decides everyone in front of it is the problem. Use it as a single solo encounter for a low-level party, or run a sounder of three or four for a mid-level one.

Gore is plus 5 for 2d6+3 piercing. If the boar moved at least 20 ft. straight toward the target, add another 2d6 piercing and the target falls Prone. Once a target is down, the boar goes for the next thing that moves loudly. Bloodied Fury gives the boar Advantage on melee attacks when it hits half HP (21), which means it gets more dangerous as it bleeds out. Charge the squishiest target on the board, trigger the Prone, and the boar has positioned itself for a second turn hit.

Panic triggers are simple. At Bloodied the boar starts looking for a way out, and torches in its face or thunder damage send it crashing back into the brush. It will not chase the party uphill, into water, or through fire. If it has young nearby, all of this reverses: it dies first, defending them.

Stage the boar by sound. Have the party hear something heavy snapping branches for two rounds before they see it, then have it explode out of the treeline already mid-charge. Beasts are about velocity.