Lion

A lion as ally is most often a druid's wild shape, a ranger beast companion, or a sacred animal bonded to a temple of a sun or hunt deity. The stat block has no listed attack, so as a companion treat it as a Large beast with a multiattack-flavored unarmed strike at the GM's discretion, and emphasize what the lion does have: 50 ft. speed, Stealth +4, Perception +3, and the visual presence of a Large beast walking calmly next to the party.

The mechanical contribution is mobility and intimidation. A lion pacing into a frontier town parts the militia without a word. A lion at 50 ft. of speed outpaces the party's mounted scout. If you want a real combat number, pull the cat from a higher CR cat statblock for one specific encounter and tell the player the lion has grown into its strength since it bonded.

Out of combat, build the bond in specifics. The druid sleeps with one hand on the lion's flank. The temple's lion does not cross the inner sanctum threshold because that is the rule. Concrete details like that turn a stat-line companion into a campaign character.

Name the lion in session one. A nameless lion is a prop. A named lion is a death the table will mourn.

A lion is a CR 1 ambush predator with 22 HP, AC 12, walk speed 50 ft., and Stealth +4. The stat block lists no actions, so resolve the lion's bite as a standard unarmed strike for a Large beast and lean on the speed and stealth instead. The encounter is the charge, not the trade. If the party sees the lion first, they win. If the lion sees them first, somebody is on the floor before initiative matters.

Set up the surprise. Tall grass on a savannah trail, a rocky overlook above a dry riverbed, a ruin reclaimed by the wild. Roll Stealth at +4 against passive Perceptions; if the lion wins, the first character within 50 ft. of its position is grappled and prone before they get a turn. That moment is the entire fight at low levels. A first-level rogue down to 0 HP from a single charge is a teaching moment about the wilderness, and it is what the lion is for.

Run them in pairs or prides. One lion is a quick kill for any party past level 2. Two lions splitting the party's attention, with one charging the cleric and one pinning the fighter, is a real fight at levels 1 to 3. Pride hierarchy also gives a free retreat trigger: drop the alpha and the rest scatter at 50 ft. of speed, and the party will not catch them.

Don't fight to the death. A wounded lion breaks off, runs, and remembers the smell. If the campaign returns to that region a level later, the same scarred lion can be back, stalking the party instead of charging. That continuity is worth more than the 200 XP.

Describe the sound before the sight. A cough in the grass, a low rumble from the rocks, then nothing. The save against being surprised is the players paying attention, not just the dice.