In 3v3 and when he is solo leftover in TW you need heal immunity, TM reduction and a stun. I use Cad lead, 88 and Greedo. Jyn Cassian and K2 also work but its less reliable because you have to get lucky with exposes.
I was remodding him last night and realized with 6e mods he will be a true monster. My current has 34k health. With 6e should be able to exceed 55k or more and when he gets that high you wont be able to kill him as quick and he will heal to full and cleanse himself. Will have to use a full team to kill him solo.