How to deal with the drill mech?

[DGDobrev]

That is a good tactic for normal difficulty, well done The problem is that on impossible difficulty the boss has a total of 98K hp (1+2+3 position) and using 1 tank +4 ranged units will make them prone to a gun shot (which is the highest chance attack for the boss if there are 2 units in the same line), which is highly undesirable...