Badger

A badger as ally is a beast master ranger's companion, a druid's small woodland friend conjured by Find Familiar (alternate form), or the cherished pet of a hermit NPC the party is trying to befriend. With a 13 Passive Perception and Darkvision 30 ft., it's useful as a sniffer in burrows, sewers, and undergrowth that humanoids can't squeeze through. The 5-foot burrow speed lets it tunnel into loose earth, which is great for finding the edge of a buried wall or following a fox to a den.

In a fight, a badger ally has 5 HP and contributes nothing meaningful. Don't put it in the front line. Use it as a scout, a tracker (rule that it gives Advantage on Survival checks to follow a recent scent trail), or as the heartbeat of a roleplay scene with the NPC who owns it. If it dies in combat because the party led it into a pack of gnolls, that's a story beat, and the NPC will hold it against them.

The most useful badger trick is the bond. A ranger who genuinely loves their badger and refuses to retreat without it changes how every cave encounter plays. Build around that. Ask the player what the badger's name is in session one, and remember it.

A badger is a CR 0 set piece, not a fight. It has 5 HP, AC 11, no actions on the stat block, and a 20-foot walk speed. The mechanical truth is that any first-level character one-shots a badger on a hit, and a badger lands almost nothing back. So don't run a badger as combat. Run it as a rules-of-the-wild moment.

A single badger guards a sett. The party is travelling and the rogue steps too close to a hole in the bank. Roll a Wisdom (Animal Handling) or Strength (Athletics) check at a low DC for the rogue to back off without provoking. If they fail, the badger boils out, latches onto a leg, and gets stomped to death in one round. The party gets a free skirmish, no real risk, and the druid at the table feels worse about killing an animal than the wizard feels about dying. That guilt is the encounter.

For more pressure, scale by quantity. Three or four badgers around an old burrow network with a 5-foot burrow speed means they pop up in unexpected squares each round. The party still wins easily, but they spend resources, eat the inconvenience of attacks of opportunity, and burn a few minutes of session clock on something that isn't a goblin. A swarm of badgers is also fair: rebuild as a Swarm of Tiny Beasts (use the rat swarm chassis) and call it a maddened sett.

Don't roll initiative for one badger unless the party started it. Describe the snarl, give one save or check, then resolve in narration. The badger's whole job is to remind the table that the wilderness has teeth, even if those teeth only deal a single d4.