There are 10 creatures which you need to ride (Press Y to mount when prompted).
Here is a full guide of creatures, credit to powerpyx (link at bottom):
Fathier (Cantonica, on the beach) – A horse-like creature with long horizontal ears.
Bantha (Tatooine, roaming around in Jundland Wastes, Mos Espa and Mos Eisley) – Like wooly mammoths with curved horns.
Dewback (Tatooine, outside Chalmun’s Cantina next to a Bantha) – A giant green lizard.
Ronto (Tatooine, next to the landing pad in Mos Eisley) – Large dinosaur-like creature with big ears and two horns.
Kaadu (Naboo, in the Gungan city in Lake Paonga and in the story level Episode 1 – Outmanned But Not Out-Gungan-ed) – Dinosaur-like creature with a giraffe colour scheme.
Orray (Episode 2 – Petranaki Panic level) – Large dog-like mounts being ridden by Geonosians in the arena.
Reek (Episode 2 – Petranaki Panic level) – The large creature which looks like a rhino. You can mount it in the second part of the mission after you’ve defeated all three creatures.
Tauntaun (Hoth, everywhere inside Echo Base) – Lizard-like creature standing on two legs with two short arms.
Luggabeast (Jakku – Niima Outpost. To spawn it, first finish the side mission ‘Luggabeast of Burden in Jakku – Tuanul Village. It will then spawn near the landing pad in Niima). – Large four-legged animal with a blue rectangular head.
Orbak (Kef Bir. Start the side mission ‘Untitled Orbak Game’, which will spawn the Orbaks on your map. Mount one to tick this creature off). – A horse-like creature with tusks.
Credit:
https://www.powerpyx.com/lego-star-wars-the-skywalker-saga-t...