Grunties are pig-like creatures that players of The World can raise in Root Towns. Grunties are kept as pets, and act as guild mascots and "greeters" to people visiting foreign guilds.They manage guild @HOMEs and take on the appearance and personality of the guildmaster. Grunties (not guild mascots) can also be ridden when mature enough.
To rent a Grunty, talk to the Grunty Renting NPC. You can only have one Grunty at a time.
You will only be able to rent the default average Noble Grunty.
You can also raise your own grunty from the same NPC, but they cannot be ridden until mature. Check the info on grunties on the link above to see what food is required for which gruntie