how am i supposed to defeat ares last in the exo mech fight

[Coopatroopa]

in the recent calamity update, the exo mech XF-09 Ares was given a new drop, that being Ares' skeleton. I really want the weapon and all i have to do to get it is to defeat ares last. problem is, my character is an endgame summoner and my minions only target ares, making it the first to go down each attempt (and trust me, i have tried whips). even without any non-accessory minions, he still goes down the easiest. so what am i supposed to do? am i just not going to be able to get the weapon? or is there a specific strategy on how to do it

[Elamit2003]

amulet of many minions lets you change minion ai to your liking with a special panel