The more i read the sadder i become, because apparently the last 5 chapters will never be translated :(
Edit: Fuck i though the LN was done but apparently its missing half of volume 5, good news its that translator its alive so its possible this year or the next one will see those missing chaps...
Sap: gradually weaken or destroy (a person's strength or power).
It's not specifically you that does that sapping (which would be draining instead), in this case it was herself overtime due to maintaining the fireball effect and in the air.
The magic circles was just nonsense to waste time.
The other weight might be from bones, i doubt you can pump your bones full of poison, at beast coat it.
And ye, not dead until he turn to dust like the previous Upper moon that would not die even without a head lol.