On a regular server this might not be such a big issue, but on a high population high level merged server this ability is completely inappropriate.
1 mana do do an instant 7% dmg to a wall every 10hours with no possible way to counter it and only against Lich players ? Are you kidding ?
How in any universe is this ability reasonable on a competitive server ?
Let just run some quick numbers , say 10 people with Tiadrin at level 35, on a merged server decide to coordinate their efforts. Hardly outside the realm of possible.
10 *7% hits at the same time that reduces the wall down to 48% of maximum HP , more than half its HP in one go ! For 1 mana ! No retribution ! No Risk ! And you can do it again in 10hours ? Are You Kidding ?!
10 hours rolls around the wall has maybe healed 2-4% depending on level
So wall starting at 52% gets hit again
Boom were now down to 25%
Bit of healing 29%
Another 10 hours
In less than 2 days this mechanic has put 2-4 weeks or more recovery time on someone's wall and they can't do anything about it. The wall is now so low that a single dwarf seige attack can send them back to the capital.
It's not like Lich have significantly better wall defence options to warrant a way to take them out without risking ANY troops.
At the very least using this ability should flag the user for revenge the same as if they'd tried to raid the city, there has to be some counter to an ability that has the ability to all but remove players from a city.
Ideally this ability should either be removed (best option) or changed so that it does a flat dmg amount not a % and Tiadrin can only use it during a wall attack(providing no loot like a Siege weapon) not in adventure mode, allowing for troop risk and revenge.
Or honestly ANYTHING that gives a Lich player some way to either counter, defend or mitigate against it.
Being forced to leave a city for a month or change races is not a solution when you've invested in a Lich wall defence.
Please make Cleanse the Land a more reasonable and fair ability.