Imuune spell will make the troops immune to damage just like grand wardens ability.
Offensive-immune spell can help to escape situations where hogs and miners jump into a series of gaint bomb if the warden is still behind or ability is already used . it can also help to deal with the giga bomb.
Defensive- For the deffensive point of view it must make the buildings in its radius also immune to damage
it would be 2 housing space Dark spell