Currently, the defending side of every battle seems to be at a disadvantage due to hero equipment, new pets, etc. However, to slightly even the odds/playing field, the Clancastle could get a buff in its defending function by also dropping the spells stored within, boosting defenses and clantroops or weakening attacking troops depending on which spells are stored inside.
The main concept would be that supportive spells (rage, healing, haste etc,) would drop directly on top of the Clancastle while destructive spells (earthquake, poison, freeze etc.) would drop down onto the troop position that triggered the Clancastle.
Siegemachines however I wouldn’t include due to implementing/ functionality issues (like what the hell is the balloon supposed to do? Float midair during an air attack forced to await its own demise at the hands of old age?)