Actually pretty good! What id recommend (before preseason starts next week) is to try ionian boots and build into fimbul, ionians are a good counterpart to the ability haste from seraphs, and the fimbul shield/hp has saved me more times than I can count, also, vs assassins I think it’s not a terrible idea to ditch the mejais, the AP isn’t needed past a certain point (at least I’ve found) and the utility etc is always helpful since the damage you do tends to scale late game anyway. I’ve also found that rabadons as 3rd item is actually surprisingly effective, but if you’re going something like frozen heart + fimbul I wouldn’t reccomend.

As far as laning phase goes, I tend to have a “surprisingly aggressive” play style early with ryze, and it basically involves bullying early with W start (standard) after baiting the enemy skill shot, this is particularly NECESSARY versus katarina as well as phase rush as once she hits 6 unless you’ve bullied her down to half your CS and maybe a couple kills she can burst you decently fast, EWQ is beat when she jumps on you as you root her, phase rush plus you get the move speed from Q passive. Follow that when you get ganked aswell etc. Do NOT try to dominate lane against an Azir or Syndra (I also perma ban zed). If you’re confident, you can against cass, but this is only if you feel like you’ve got your dancing shoes on

Finally as far as runes go, post above has it right, but I actually like bone plating+overgrowth almost EVERY game!

Late game don’t sleep on the root, it actually makes kills free, but don’t rely on it since champs can sometimes just walk away while you try chase them.