Eagle

An eagle on the party's side is a scout, a ranger's companion, a druid's wild shape, a paladin's totem. Run it for speed and sight, not damage. The 60 ft. fly speed and passive Perception 16 make it a superior scout: it circles a fortress in two rounds, watches a treeline from above, and brings back what it spotted to whoever it answers to.

In play, the eagle's job is to see things the party cannot reach. It can make a Talons attack (plus 4, 1d4+2 slashing) if enemies have arrows for it or if it must defend itself, but a 4 HP creature with AC 12 should almost never engage. Keep it perched or circling. Ask what the player wants to know about the terrain ahead, roll a DC 12 Perception check (the eagle can handle that easily), and hand back one specific detail: a patrol route, a second sentry, a gap in the wall, a fire in the forest.

As a ranger's beast companion or a druid's wild shape, the player narrates what the eagle sees. As a wild bird serving the party, the GM describes its findings in clean, tactical language. Either way, the eagle reports and withdraws.

Give the eagle a name and one specific habit that makes it memorable. Drops feathers into the cleric's pack. Hates one NPC for no clear reason. Perches only on the tallest thing. These small touches carry the character of the bird through the campaign.

A solitary hostile eagle is a minor annoyance, so contextualize it. Run eagles defending a nest, a flock driven to attack by a hag, or a swarm narrative where the real threat is the fall, not the bird. One eagle with 4 HP and 1d4+2 slashing damage does not make an encounter; something else does.

Use eagles for pressure and mobility. While the party climbs a cliff face, three eagles dive at them, calling for Athletics or Acrobatics checks to hold their grip and position rather than forcing melee exchanges. The fail state is the rope, the fall, the dropped supplies, not HP loss. The eagles stay aloft at 60 ft. fly, spot the party first with passive 16, and choose when to dive.

If an NPC is driving the eagles with magic, that's the real encounter and the birds are the spell effect. A fire spell, a Hunter's Mark, any decent area damage scatters them. Eagles defending a nest will pursue to the cliff's edge and disengage into the forest; eagles under compulsion fight until their master is killed or they take half their number in losses. A perceptive PC can tell the difference with an Insight or Nature check.

Don't roll initiative for a single eagle. Resolve it as narration or a skill check, and save the dice for the terrain.