I am really not sure, it looks to me like a flush / turned straight. But then why wouldn't he have raised the turn with a straight. Not all players are clever hey.

I would definitely not check/call. There is nothing a loose passive will bet into you that you beat here. I don't think you should ever check into a loose passive with a hand that will beat most of Buttons holdings until he raises.

Bet/fold or Bet/call. I am not sure yet though. would he play 8-x in this fashion? He is passive so he wouldn't bluff raise this river after MP calls I think.

He is passive, so would he think his 8-x is good?

True