To nearly double the mana ratio on your q, and to make your autoattacks baby q's.

Thought about doing this; would only do it if the enemy wasn't building any armor. Otherwise it's better to focus on magic damage & pen items so that more of your damage gets through.

Muramana's toggle effect deals magic damage with single-target abilities (of which, Ryze has 2, 1 with a negligible cooldown.)

i have a question about it, if i have an archangel's staff, and i get the muramana, do both items passive ( both grant 1000 mana) stack? or i just get 1000 mana instead of 2000?

You will gain the bonus 1000 mana from each as its part of both items. It isn't part of a stacking mana passive, though you will need to stack the mana passive two times in order to build both.

My initial reaction was "No"

Then I thought about the synergy between Manamune/Muramana and Iceborne Gauntlets (which I've started building instead of FH on Ryze)

That's a LOT of burst splash damage every few seconds on top of an aoe slow.

Yeah, I'm REALLY liking this idea

Muramana's toggle adds magic damage to your auto-attacks. Which happens to be the damage type that doesn't care about armor at all, making lightly armored targets completely unnecessary for weighing it's effects. You're also liable to build magic penetration on Ryze, and enough mana for the actual mana to AD ratios offered by Manamune to count for something on Ryze.

But seriously, the magic damage you get with this is ~200 per hit on Ryze, were the AD it gives won't likely exceed 100 on anyone, ever.

Yes, it's awesome. I make my first tear a manamune, and get AA as soon as it evolves. As for iceborn instead of fheart, maybe. Or you could just get fheart and lichbane. RoA and AA on ryze plus lichbane's flat AP gives you a massive chunk of physical and magical damage to add to muramana's 100+ ad and mini Q proc. He becomes murder.

True but when you combine it with the proc on Iceborn Gauntlets...

The proc on Iceborn is based on AD, Manamune/Muramana grants AD based on mana, the two synergize insanely well while still boosting Ryze actual spell damage due to them scaling on mana. Not to mention his AP ratios themselves are not terrible (and actually higher than his mana ratios on his E).

5% CDR and a little armor are definitely worth the tradeoff for a burst of additional "free" aoe magic damage and an aoe slow. The proc has a 2s internal cd which matches about the cdr of Ryze Q when going into his typical alternating spell rotation. Iceborn will be triggering every time Ryze Q's

Manamune/Muramana makes

You seem to forget the proc on iceborn is BASE damage.