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I've encountered such glitches, but I remember it happening in WOG. There's even an option there that increases the damage of towers... it's influenced by:
1. How many weeks in a row you own the castle (it increases with each new week)
2. The more defenses you withstand, the more damage... and + the amount of HP defeated by the defenders...
P.S. In short, towers gain some kind of experience... I personally managed to get the central tower to deal 300-350 damage.
I wouldn't agree about the experience; there were times when a hero attacked me, about 8 times stronger in terms of the power of his royal army, and I won due to the colossal damage from the towers! And conversely, some time after that, a computer attacked with a much weaker army, and the damage became normal. Is there an explanation for this, or is it just a bug?
"Единственное, что можно сказать с уверенностью об удаче - она изменит..."