I tried it on orianna last game, my only other mana item was a lich bane and it gave me a nice chunk of ap and a decent shield

I think Seraph's Embrace is amazing on anyone who can get a Rod of Ages or maybe a Banshee's Veil. It gives nice mana, AP from the mana, some health, and some extra AP/MR.

Can I ask for the rest of your build and why you did not put in any other mana items? After all, you just spent 2700g on an Archangel's Staff.

And, according to LoL Wiki, you need 3000 mana for the AP to equal Rabadon's in terms of power (not to mention the mana shield).

I take it on champs that I buy Lich bane and RoA on at the same time. (Ex: Nid)

OP on the already tanky ryze who builds 2 Catalysts and a tear early, then goes ROA, Embrace, and a Banshees veil.

Lategame powerhouse. Build a frozen heart or ice fist for the armor.

Last 2 items are boots, obviously built earlier, and a Deathcap. Or a warmogs if you wanna go full tank. Whatever you want, really.