Does that work? It gives him the bonus attack speed to make better use of his W and gives him some much-needed CDR and AP for his other skills, although it doesn't give him as much burst as say, Wooglet's Witchcap, it gives him a bit more sustainable damage....or am I just flat out wrong and I should be building no attack speed on Kassadin.

Nashor's tooth is a very expensive item. In the vast majority of cases, you want to build for burst over sustained damage. Attack speed gives Kass. some sustain. If you are going for a spell vamp/life steal build(or something) on him, I guess Nashor's tooth is a fine item, however I do not think you should use it if you intend to play him as a squishy, mobile assassin.

Kassadin does substantial sustained damage with riftwalk stacks, and needs maxed CDR for this purpose. Out of the three codex items, Athene's is usually most favoured because Kassadin is very mana hungry, but the differences between the three are not huge.

So Nashors tooth is less suitable for the kind of instaburst hero that Kassadin is typically played as, but is more suitable if I was say, going to build more of a AD/AP mixed build with lifesteal and spellvamp mixed in? I was thinking about Athenes, but usually after I build rod of ages and have a frost gauntlet up, I can probably use about 6 or 7 stacks of riftwalk at full mana before i run out of mana, especially since health packs also regenerate mana in Dominion.

no nashors for instaburst. but for slicing and dicing it's actually retardedly efficient.

I don't think there's a compelling reason to ever get Nashor's on Kassadin.

If you're playing Kassadin as a burst assassin, you don't have time to stand around auto-attacking because you'll get sneezed on and die.

If you're playing mana tank Kassadin, your passive takes care of your attack speed pretty handily, and you need to spend that gold on survivability, desperately so.

If you're playing AS/On-hit Kassadin, you're probably dead before you entered the fight, unless you're one hell of an exceptional opportunist... and even then, you probably would have done more damage in that same period of time with an AP build. ...but I've never played AS/On-Hit Kassadin, so I could be wrong.

I figured that Nashor's tooth made Kassadin kind of a mix between AP and AS/On-hit build, as it gives him some of the attack speed and the AP and CDR he so desperately needs. True, he isn't as fast in bursting down heroes than a pure AP build, but he does tend to be not as useless when his skills are on cooldown...not to mention the bonus mana that his w passive does so I can ult more and faster.

I don't think it was exactly useless, I was just wondering if I was just buying a completely terrible item that could be put to better use elsewhere...The bonus magic damage he gets from his w is pretty significant, I was thinking I could put it to pretty good use with some attack speed especially if theres another tank on my team to soak up damage so I don't have to worry about tanking quite as much.

Yes you can put it to better use

like defensive stats, which increases the amount of damage kass can absorb, which translates to more attack speed from his passive

I get what you're thinking. If I'm facing a mage and he bursts me for 50% of my health and I have a nashors, my attack speed will skyrocket to 2.5/s and I will activate my W and whack the absolute **** outta this guy. That's happened to me and it's hilarious...

It's an awesome concept,but turns out that as Kassadin you don't want to stick around a fight for too long. If you want to auto somebody for damage, Sheen/Lich Bane is a much stronger alternative.

Much better to build bursty and jump in and out of range to kill them though.

But really, lets face it, even if it isn't a great item on Kassadin, he's still playing Kassadin.

So it will probably work.