Here is the full list of all 24 Royal Offense achievements.
During single battle hire 300 heroes.
Get 10 Silver Medals on same mish.
Hire two holy heroes at same time.
Win any silver or gold level without any troops.
Get a diabolic number of Medals. ^T^
Get 5 gold Medals on same mish.
Get 30 kills with just one unit or hero.
Headhunt for 10000 silver.
Hire 666 dark heroes.
Kill a Troll, save the Lady.
Kill weaken enemy.
Level up any hero during mission to level 5.
Build biggest castle in kingdom.
Upgrade any weapons or armor to max level.
Hire 100 mages.
Level up any hero to level 9.
Hire 100 archers.
Earn 10000 gold.
Kill 3 enraged enemies.
Level up any hero during mission to level 3.
Kill 50 rats.
Repair any building.
Build 3 buildings.
Get the first kill.