Cockatrice

A friendly cockatrice almost always belongs to someone. A hag who keeps a clutch of them, a druid who has imprinted one as a familiar substitute, a wizard who needs a low-cost guardian for the laboratory door, an alchemist who farms them for petrification components. Make the owner the actual NPC and the bird a creature feature.

In a fight beside the party, a cockatrice is a control piece, not damage. Position it on the enemy caster's flank and tell the player at the table that the bird will go for the squishiest enemy with a Con save under +2. The bite hits for almost nothing, but a stoned cult fanatic mid-ritual is worth the entire fee for the encounter. The cockatrice will not coordinate with the party past basic "go there, bite that one" commands; it has Int 2 and the keeper is not at the table.

Out of combat, the cockatrice is a problem. It pecks at hands, panics around horses, and any failed save against a reaching finger means a party member just lost a day. Have the keeper give the party a hood for it and a clear rule: the hood comes off only on the keeper's word. Players who break the rule learn an expensive lesson about why guard animals have handlers.

Give the cockatrice a name and a single quirk. "Kettle hates the bard" is more memorable than any stat block detail.

A cockatrice is a low-CR encounter that punches like a much higher one because of one word: Petrified. The party stat block sees CR 1/2 and 22 HP, looks past it, and then a level-3 fighter spends 24 hours as a garden statue. Sell that risk before the fight by showing the party a previous victim, a stone halfling mid-stride at the edge of a farm, before the cockatrices ever fly out of the brush.

Run them in pairs or threes, never solo. The bird walks at 20 ft. but flies at 40, so the encounter is air-to-ground. Each cockatrice picks a target and does Petrifying Bite at +3 for 3 damage, then flaps back up out of melee reach if it can. The damage is a rounding error; the DC 11 Con save is the entire point. First failure imposes Restrained, which most parties react to with relief because they think they understand it. Second failure stones the target for 24 hours. Make sure the table understands the staircase before they start rolling, because it changes target priority on the party's side mid-fight.

Target the front-line martial first. The party's Con-save champion is usually the wizard or sorcerer, so a flying bird that ignores the tank and plinks the rogue will land more saves. Don't be greedy with positioning; a cockatrice that gets cornered is a cockatrice that dies in one hit (AC 11, 22 HP). Use the fly speed to leave melee even at the cost of the opportunity attack, because the bite is the win condition.

A cockatrice flock breaks the moment two of them die. Beasts at Int 2 don't make heroic stands. The survivors fly off in different directions, and the party should worry about meeting them again on the way back through.