Here is the full list of all 23 Royal Roads achievements.
Beat 100 levels with 3 stars
Help the princess return her former self
Earn all possible trophies in Royal Roads
Tame all kobolds in the Kingdom
Help all griffons return to the kingdom
Defeat all pirates in the kingdom
Sail the archipelago and dock in the Land of the Wizards
Beat 80 levels with 3 stars
Beat 60 levels with 3 stars
Make it to the Azure Shores by tunnel
Stop the disasters in gnome caves at the source
Defeat a kobolt
Beat 40 levels with 3 stars
Open the gates to Gnome Caves
Help all elf villages find ancient altars
Use elf magic
Beat 20 levels with 3 stars
Fix the bridge and move on to the Elf Forest
Help repair all settlements after natural disasters
Use your royal will
Beat 10 levels with 3 stars
Use horses
Beat 5 levels with 3 stars