Giant Lizard

A trained giant lizard is the lizardfolk mount, the kobold draft beast, or the desert tribe's caravan puller. The PC who acquired it either did so by buying it from a swamp trader, befriending a hatchling on a previous adventure, or having a druid friend hand-raise the thing. Statline aside, this is a working animal with a tongue that licks faces and a tendency to bolt at fire.

In combat the lizard's value is the climb. The party's small races, halfling rogue, gnome wizard, can ride it up a wall and onto a roof in a single round, bypassing whatever the enemy was guarding at the door. The lizard itself is not a serious damage dealer: 6 average bite, +4 to hit, no special action. Park it on the cleric, have it intercept anything that comes around the corner, and use its 40 ft. speed to drag a downed PC out of melee. Treat it as a mobility tool, not a fighter.

Outside combat the giant lizard is a slow-moving logistics solution. It eats almost anything organic, scales walls the party can't, and tolerates rough handling that would lame a horse. The downside is intelligence. It does not understand spoken instructions beyond the few words its handler trained, and it will not patrol or guard reliably without supervision.

Give the lizard a name and a feeding habit. Players adopt mounts harder when the mount has a personality quirk to remember.

A giant lizard is a low-CR ambush bite for a cave or jungle level. CR 1/4, 19 HP, AC 12, +4 to bite for around 6 piercing on a hit (the SRD entry here is bare, so use the standard giant lizard bite). What it actually contributes to an encounter is the climb speed: 40 ft. walk and 40 ft. climb, with darkvision out to 60 ft. The lizard runs along ceilings, drops onto a back-rank PC, and either lands a bite or scrambles back up the wall.

Run them in pairs or trios, and make the environment do the work. A single giant lizard against a level-1 party is a reasonable opening fight; three of them in a cavern with stalactites turn the encounter into a positioning puzzle. Have one drop on the rogue while the other two scuttle the walls toward the wizard, climbing past the fighter who can't reach them. The party's instinct will be to ready bows. Reward that, then have the next one come from a passage they didn't watch.

Damage priority is simple: the lizard goes for the smallest, slowest-looking target it can reach. Int 2, so no real tactics, but it knows what looks edible. Once Bloodied (10 HP or under), it climbs to the ceiling and waits. If the party walks past, it tries again. If the party shoots it down, it dies.

Use the climb speed deliberately. A giant lizard that fights on flat ground is a turtle with teeth; a giant lizard on a wall is the encounter you wanted. Telegraph it once with a chittering scrabble overhead before the first one drops.