Wallace would like this battle to get over with because aside from getting a piece of advice from Veda, it even warned him about something else.
[ The lamia has an experimental stage Healing Orb somewhere inside its body. You can try removing that to kill it. Also, you may want to hurry and leave this place before your mana starts being corrupted. ]
"Corrupted?"
[ Correct. You may possess a level of immunity because of your Astral Core but your subordinates do not. In any case, you can consider going deeper inside this tower after this trifling matter. You might find that place interesting. Good luck! ]
Wallace didn't mind the latter part in the meantime as he was curious about the corruption it mentioned.
If it was really that dangerous, then Percival and the lady together with him must be affected already, considering that they have been here for a long time.