League of Legends (LoL) Question: Mercurial Scimitar on AP Katarina

While definitely a possible build, it's definitely not necessary nor optimal for a Katarina, despite the AD scalings and Katarina's hatred for hard CC.

For once, the item itself isn't optimal nor efficient for the champion. Sure, it has AD and Kat has AD scalings, but Katarina would much rather invest into AP. AP is more abundant, as in, you can get more of it, and not to mention Katarina overall scales much better with AP. The magic resist is nice, but there are better options if Katarina wants magic resist, with the glaringly obvious option being Abyssal Mask.

The active component is an interesting one, because the bane of Katarina's existence is hard crowd control. Katarina's main appeal comes from Death Lotus, an AoE ability that deals a ****ton of damage, but is very easily stopped by CC. Quite frankly, the CC cleanse component will be completely redundant on Katarina. The only really detrimental time a Katarina could get CC'd is during Death Lotus, but if you cleanse the CC that cancels Death Lotus, then you still don't have Death Lotus, and your uses in a fight became incredibly limited, even if you could use your other abilities. The other thing is because of Katarina's playstyle. Even if you had CC cleanse or immunity, your aim still isn't to soak up CC. You want to avoid it. Good Katarina players won't go into a fight in the start. Heck, most of them won't even go towards the middle of the fight. Good Katarina players go towards the end of the fight so they can clean-up and get resets, and because at this point in the fight, it's safe to assume that all hard CC will be burnt by this point. If not at the end of the fight, Katarina will engage directly after CC is used.

And, even if you get an opportunity to cleanse CC in a teamfight, let's be real here, Mercurial Scimitar is a late game item if you do purchase it on Katarina, you'd much rather have Zhonya's Hourglass, because not only does it allow for you to stall for cooldowns that you most likely would have burnt getting into the fight, but it also throws the enemy team into complete chaos for a split second as they find something to redirect their attention to. You're still vulnerable after using QSS, and chances are, you'll have no way to get out of the fight, so really, cleansing CC will be useless. At least Zhonya's Hourglass gives you some sort of chance to get out of a fight or divert focus towards you. Plus, Katarina scales much better with AP, and especially with a big AP item like Hourglass.

So, pretty much, why would you want Scimitar over your other, much better options? It doesn't do anything better than the items Katarina already buys does, and if you do purchase it alongside an item, then it's just redundant. It's simply a question of why. You can do it, but why would you want to? Much like how I could bang Vapora's mum, but why wouldn't I just go for a decent woman?

You could probably just take Cleanse to deal with stuff like Frozen Tomb. Quicksilver Sash is a pretty uncommon buy on most mids but you could maybe justify it against suppression abilities like Nether Grasp or Infinite Duress. If you still need it late game you can upgrade to Mercurial Scimitar since Kat actually has some AD scalings.

Avoid that build path when possible though. AP items are going to be much better for your build than Mercurial. Consider whether Zhonya's Hourglass, Mercury's Treads and/or Cleanse could be used instead, freeing up an item slot for another AP item.

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