Driller tactics is needed

[DGDobrev]

Well, you can try to "mold" the boss behavious in battle if you decide to do it with 5 troops. If you have 2 good tanks, you can put them near one of his hands with stone skin on to minimize the losses. In this case the boss will have a higher chance to strike both those targets on attack rather than use his gun or summon droids. That may buy you some extra time to drop him down.