Giant Fire Beetle

A friendly fire beetle is a pet. The dwarf cleric grew up on a mining settlement where every household kept a beetle in a wire cage as a nightlight. The druid wild-shaped into one and made friends. The wizard's apprentice raised them as a kid and one rides in his pocket. Run it as flavor first and combat almost never.

The beetle's value is the light. Two glands above the eyes shed dim light in a 10 ft. radius, and that light cannot be easily extinguished. The party never runs out of torches as long as the beetle lives. In a dungeon with magical darkness, the beetle's natural glow can serve as a sanity check: the players see it dim or flicker and they know something has stripped the magic from the room. The Blindsight 30 ft. also makes the beetle a passable invisible-creature detector for any party that bothers to watch its reactions.

In combat, do not put the beetle in the line of fire. 4 HP folds to a stiff breeze. If the player insists on having the beetle help, treat it as an improvised attack at +1 for 2 bludgeoning, and remind them that the beetle dying means the room goes dark mid-fight. That's the whole tactical layer.

Give the beetle a name and a habit. The one that nests in the wizard's hat, the one that only glows when it likes the company, the one that hisses at undead. Players will mourn a beetle they named.

A giant fire beetle is a light source with legs, and the encounter is the room around it rather than the beetle itself. CR 0, 4 HP, no actions on the sheet. The players will kill it in one hit. Your job is to make sure that hit matters.

Use beetles as scenery and as bait. A nest of three or four giant fire beetles in a cave wall produces enough light to read by, which means the party either has to extinguish them (squashing each takes a turn and provokes any nearby actual monsters) or accept that they are now visible to anything else in the dungeon. Place them in the chamber before the boss fight. The beetles are alive when the party walks in, and the boss can use the light. The moment the party kills them, the chamber goes dark and the boss has Blindsight or Darkvision and the party doesn't.

Mechanically there is almost nothing to run. AC 13, no Multiattack, no traits. If the beetle has to attack, treat it as an improvised slam at +1 for 2 bludgeoning. The Blindsight 30 ft. is the one real feature: a fire beetle in pitch darkness still knows where the rogue is. That makes a swarm of beetles a tripwire alarm system more than a combat encounter. They scuttle, they bite, they get crushed, and the noise alerts whoever owns this cave.

If your party is level 1 and you genuinely need to throw fire beetles at them as a fight, run six of them in a 20 ft. radius cluster of glowing carapaces. The fight is short, the lighting is dramatic, and a level 1 wizard with 6 HP can still die to a string of unlucky bite rolls.

Squash one and have the light gland keep glowing in the rogue's hand for an hour. Players love a free torch they pried out of a dead bug.