One of the cool things about Dragon Quest XI is that players will have an opportunity to ride different kinds of mounts that are scattered across Edrea. Aside from the usual horse that players get at the beginning of the game, there are monster mounts that you can you hop in and help you travel faster from one location to the next. Sometimes, there are other mounts that have different abilities that can aid you in getting that secret treasure while others will help you in clearing out debris to access a secret area.
Source: N4G PC Dragon Quest XI Guide – Mount Olympian Trophy (List of Mountable Monsters)