Pteranodon

A pteranodon as ally is a primal-party scene: a druid's wild shape, a ranger's beast companion via homebrew, a dinosaur-rider tribe that has loaned the party a mount for one flight. The pteranodon does not converse and does not problem-solve. It tolerates the rider because the rider has trained it to.

In the air, run the pteranodon as transport. 60 ft. fly speed lets it cross a ravine in two rounds, scout a valley between sessions, or carry one Medium PC on a single dramatic crossing. It has 13 HP, so it cannot soak archery from below; if the party flies it over a hostile camp, somebody is going to roll a longbow attack and the pteranodon is going to fall. Plan for that.

In combat the pteranodon's stat block prints no actions, so any attack it makes is a table-agreed adjustment (the natural read is +3 for 1d6+1 piercing using its Dex). It is not a combat asset. It is a positioning tool. Use it to drop a rogue onto a tower roof, snatch a dropped item out of a chasm, or carry a message faster than a horse. Its 10 ft. walking speed means it never fights on the ground; if a fight breaks out near the landing pad, the pteranodon launches and circles until called back.

A wild pteranodon kept as a mount has a recall range of about a mile and a memory of about a week. Druids and rangers can stretch this with the appropriate spells. Without those, the pteranodon is a rental, not a companion.

Have the pteranodon scream once, loud, when it spots a predator the party hasn't noticed yet. Then describe what the predator is.

A pteranodon is a flyby beast with no actions in its SRD block, which tells you exactly what it is: a CR 1/4 environmental hazard with a 60 ft. fly speed and 10 ft. of walking that exists to harass parties in the air. 13 HP, AC 13, Strength 12, Dexterity 15. The party kills one in two hits. The point of the encounter is the swarm, the fall, or the swoop, not the stat block.

Use pteranodons as ambient pressure during a cliff climb, an airship boarding, or a jungle traverse. Run three to five at once for a level 1 to 2 party. The walking speed of 10 ft. means a pteranodon that lands is half-dead already, so they do not land. Open with a high pass: each pteranodon flies 60 ft. straight at one PC, makes whatever bite or beak attack the table agrees on (the cleanest read is +3 to hit for around 1d6+1 piercing using its Dex), then flies the rest of its movement back out of melee range. The party gets one round of opportunity attacks before the next pass, and ranged characters get to feel important.

The encounter's real teeth are the surroundings. A failed concentration save while a wizard is hovering on Fly. A failed Strength check on a rope bridge. A panicked horse that bolts because the shadow passed overhead. Run pteranodons during another encounter for free atmosphere, not as the encounter themselves. They make any other fight harder by occupying the air and forcing somebody to hold a bow on them.

Pteranodons are Intelligence 2 and Wisdom 9. They flee the moment one drops. The flock breaks, scatters into the canopy or the cliff face, and the survivors do not regroup. Do not have them stage a vendetta; they're animals.

Describe the dive as a shadow falling across the map a beat before the attack roll, not after. The shadow is the threat. The bite is the punctuation.