A companion creature is a wild ally that adventures with the characters. Each companion has unique traits and actions that make them a great ally, but they are still wild creatures. They are difficult to control on the field of battle and there is always risk that they will bite the hand that feeds them.

Ferocity

Companions are dangerous creatures. Though often more docile than their wild counterparts, they aren't fully domesticated. Each companion's Ferocity is a measure of their tenacity and fury, and of how those qualities build in battle. As a companion's Ferocity increases, they may gain access to powerful new features, but they also become more difficult for a caregiver to control.

If a companion isn't Incapacitated at the start of their and their caregiver's turn, their Ferocity increases by 1d4 + the number of hostile creatures within 5 feet of the companion that they can sense. For the purpose of building Ferocity, a group of creatures that share a single stat block such as a Swarm of Rats count as one creature. Ferocity builds round after round during combat, and there is no maximum to the level of Ferocity a companion can gain.

Rampage

After rolling to increase Ferocity at the start of their turn, if a companion has 10 Ferocity or more and is not Incapacitated, they run the risk of entering a rampage. The companion's caregiver can make a Nature (Wisdom, Intelligence, or Charisma) check (no action required) to try and stop their companion from entering a rampage. To make the check, the caregiver must not be Incapacitated, and the companion must be able to see or hear the caregiver. The DC for this check equals 5 + the companion's current Ferocity. On a success, the companion acts normally on their turn. On a failure, or if the caregiver doesn't make the check, the companion enters a rampage.

When a companion enters a rampage, they immediately move up to their speed toward the nearest creature and attack that creature with their signature attack (the melee variety if there is a ranged variety), dealing extra damage equal to half their Ferocity if the attack hits. If at least one ally and one enemy are nearest and equidistant to the companion, the companion's caregiver's player rolls any die. If the result is odd, the companion attacks an ally. If the result is even, the companion attacks an enemy. The caregiver determines which specific ally or enemy the companion engages, and can choose themselves.

A companion who can't reach a creature to attack while in a rampage uses the Dash action to move as far as they can toward the nearest creature. If a companion cannot sense any potential targets, they move as far as they can in a random direction determined by the GM, avoiding danger.

When a companion who is rampaging resolves their action or ends their turn, their Ferocity resets to 0 and they are no longer rampaging.

Reducing Ferocity

Combat's End. When a combat encounter involving a companion ends and the companion isn't dying, the companion regains hit points equal to their current Ferocity, and their Ferocity drops to 0. The DM determines when a combat encounter formally ends, typically at the point when creatures stop acting in Initiative order.

Dying Companions

When a companion is reduced to 0 Hit Points, they are dying and make death saving throws just as characters would. Characters thus always have a chance to save their companion's life. If combat ends while a companion is dying, their ferocity drops to 0 but they don't regain Hit Points as they would if they were not dying.