Yoda is really good in arena. You open with him giving your whole squad tenacity. Makes you immune to the likes of sids dots or insures dooku or daka can't stun you for 2 turns. I find it invaluable.
Follow the strategy that was given for me. Keep retreating till you get yoda with low damage toons, preferably one of the barris and use the health cutting trick. It's trail and error I'm afraid. I have been trying for days and no luck. I think I. Just gonna give up and wait till I have igd.