Matezoide's first sub (both actually) has very dubious interpretation. I will read it as "change current action to Rock Slide and following ones with Leaf Storm and Seed Bomb if Applicable" since that is what he intended.
since it IS a VERY dubious sub, I will give you 24h to change your actions accordingly. If nothing changes 'til then, I will ref with your current actions.
I wouldn't bother trying to save Seraph. Speed drop is gone, so it can fire off a Flamethrower before going and Mystic can use two Fire Punches. By my calcs, that plus my actions should leave Metagross with exactly 20 HP left, which we can easily chip off next round.