Muramana is a great items whem paired with Iceborn and mana masteries endgame it increases your Q, autoattack, and E damage by 40-160 from just the toggle and gives you 75 AD on top of that. So it is an IE for 2100 with a 400 damage increase on your burst combo from the toggle (Q, AA, E all work with toggle). But you have to get some major MP5 regen if you want to be able to use the passive (aka getting blue buffs or Nashor's tooth or both!).

I like running Berk, Muramana, Iceborn, Nashoor's, BOTRK, MoM so that I don't just explode to magic damage with 86 MR by yourself +raka passive+bulwark=129 MR and about 2200 HP with the shield you can take a burst cycle and still be shooting. Also my build hits 40% CDR (1 CDr per level glyph and mastery) so that you can get the most out of both Muramana+BOTRK. BOTRK is because I am not getting any %pen hoping that one of my mates will get BC and i need some way to deal with high HP takes 1.5K-3k hp = BOTRK is doing 60-120 damage per hit just from the passive which is more than Bloodthrister. Also the Active adds to your burst and kiting abilities.