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