Deathcap is one of the perennial caster items in League of Legends. Not only does it give an enormous amount of ability power, but it also increases all of your ability power (including what it grants) by a whopping 30%. This seems so ridiculously powerful! Even though it's expensive, 30% increase in AP is such a huge boost to damage that it can't be beaten.
Is this really the case, though? In Summoner's Rift, I completely agree that Deathcap is a great item. In Twisted Treeline, Wooglet's Witchcap (the replacement item for Deathcap) is also incredible. However, in Dominion and ARAM, the fast-paced action and frequent conflicts change the nature of the wizard hats considerably.
What Deathcaps are good at
Before I began writing this article, I crunched a whole lot of numbers on various builds, but I won't bore you too much with the hard math. Deathcap is useful for one thing, and that one thing is quickly becoming less and less common. That one thing is blowing up glass cannons.
Consider the typical ADC or glass mage. He might have, in a typical midgame scenario, 1500-1800 HP and around 40-50 magic resist. In this kind of situation where HP is fairly low, Deathcap is fantastic because it facilitates those big burst combos. If you have around 200-250 AP with your Deathcap (including the 30% bonus), you stack on big chunks of damage. With Sorceror's Shoes, you shell out a three-nuke combo doing 400 damage or more each. If your target has taken even moderate damage from anything else such as your own harassment or some softening by allies, you are fed enough to have an extra item; if someone on your team is carrying Abyssal Scepter or some other way to increase your damage, you are very likely to melt that ADC with your full combo.
In the late game, there's some falloff becaude of HP from leveling and common items like Banshee's Veil, but it's also likely that you'll have a Void Staff to punch through a lot of magic resist. Also, Void Staff itself gives a lot of AP, and you get 30% more thanks to Deathcap. You won't quite blow up a glass cannon (unless she didn't build a Banshee or other magic resist item), but your full burst will take her from full to nearly dead. In that situation, it's almost as good since she can't stay in the fight at all and must retreat, lest she get dived on by your bruisers or tanks and killed.
Even mages that spam rather than burst (like Cassiopeia) benefit a lot from Deathcap since it makes each spam hit really dangerous. Cassiopeia with a Deathcap, Void Staff, and one more AP item feels really scary, since each hit from Twin Fang feels like a shot from an ADC and she can spam similarly fast.
When Season 3 started and the big item changes hit, I had no idea which way was up. I was buying items almost randomly for quite a while, and because I played a lot of Dominion, I didn't really have a lot of "pro advice" to fall back on. I realize there's a community for Dominion players out there, but it is not the same as being able to watch pro matches, featured streams, and so much more with just one Google search. It took me a long time to really feel out how to play the game again.
It was not long before the Dominion community observed that buying HP was very good and that natural tankiness (from abilities and such) was very strong. Although Season 3 hasn't supplanted glass cannon builds entirely, they are much less effective since buying HP is so much cheaper. Also, there are a lot more options to do it. Blackfire Torch was the bane of Dominion, and after that, Black Cleaver was too strong. Both were nerfed, but they are both very strong and continue to be a big force in the current metagame.
However, I'm here to talk about SR/TT/ARAM too, and since we're discussing caster items specifically, I need to bring up Liandry's Torment. Liandry is an evolution of Haunting Guise; it provides 15 magic penetration in addition to bonus HP, some ability power, and its health-shred passive. It deals 2% of current health per second for three seconds, doubled if the victim is under any movement debuffs. Its big brother Blackfire Torch deals 3.5% of maximum health per second, which is incredibly frightening.
In the big meta scheme of things, and especially in non-SR gametypes, building more like a bruiser tends to be just better overall. Getting more HP tends to give a lot of value, its cost is lower, and there are more ways to do it. Rylai's Crystal Scepter and Rod of Ages continue to be big favorites and were made significantly cheaper in Season 3. Aside from ADCs, most physical damage characters are building more efficient tanks with items like Black Cleaver. Even a lot of ADCs are building Trinity Force and other semi-tanky items.
What this all means is that in Season 3, a lot of characters got a lot harder to kill. The average enemy champion has 200-300 more health (if not more) and 40-70 more magic resistance than before. That extra survivability also turned into a meta shift toward mages that deal more sustained damage, have some kind of innate survivability, or serve more utility functions. Being able to burst someone from 80% to 0% in one go just isn't feasible except in the SR midgame. If you're on any other map, though, it's unlikely that will ever be an option except in games where you are dominating.
Liandry's Torment is a specific interesting example because I buy it a lot and think it's underrated. In situations where enemies build moderate amounts of MR (one item), it is a lot better, since Liandry + Void Staff increases effective damage dealt as it punches through so much MR. At higher MR, it actually loses a bit of its bite; the difference between 150 MR and 135 MR is a lot less significant than the difference between 25 and 10.
You would think that the main reason to buy Liandry is the passive, but it's actually the passive, the penetration, and the HP. It really isn't worth buying for just the passive. At high HP totals, it's amazingly good -- 75 HP per second to a target with 3000 HP or about 225 total damage if it runs completely between each spell hit, doubled if it hits a slowed or stunned target. Unfortunately, that isn't the whole story. That damage is resisted by MR and becomes less and less useful as the enemy's health drops. It's fantastic for harassment, and even the 200 or so damage it'll deal through the course of a typical late game fight is pretty nice.
Deathcap gives more than twice the AP of a Liandry, though, and if someone has 200 AP with Liandry, he'll have around 350 with a Deathcap instead. That extra AP, when considering for MR, is still going to deal comparable damage to hard targets and more to soft targets or those who are already damaged.
That's the thing, though. Liandry's magic penetration works similarly to Deathcap's 30% bonus AP (somewhere between 5-12% more damage) but applies to all magic damage, including base spell damage and its own passive DoT. For characters with lower AP ratios, Liandry looks better and better. It also works great for characters that use area denial, like Morgana's pool or Zyra's plants (and yes, the plants apply the Liandry passive). People might get tagged only lightly by these abilities, and the burn does a lot more in those situations.
So back to the Diana thing: Is she better off building Liandry? She has poor base numbers on her Crescent Slash (unfortunately nerfed), but the ratio is average at 0.7. Her overall combo ratio, combining at two of her orbs, her Crescent Slash, her passive, and her ultimate, is pretty high at 2.2. Additionally, her ultimate has somewhat lowish base numbers for a typical spell nuke as well, so AP really is a lot of her damage. Add in a second dash and a third orb, and it's 3.0; add in a not-so-improbable second slash and third ultimate hit (it's a bit of a trick shot, but it happens in real games) and she's dealing 4.3.
The flip side of this is that Diana needs to close distance. To deal her big combo, she has to be in melee range of her enemy, and even in the laning phase that's likely to end up eating a turret shot in order to clean up. In a teamfight, she's likely to get melted even though she's got a shield. Extra HP helps, but the reality is that extra HP isn't enough, either. I've survived a lot of fights at incredibly low HP totals when I knew Liandry's HP made the difference. Unfortunately, none of them was playing as Diana.
Long story short: I hate the Diana nerfs.
However, for all other mages and especially characters like Cassiopeia or other characters that deal lots of damage in little hits, I think Deathcap is not something you want to rush. I'd even go so far as to say that, in the current meta, the glass cannon-type mage is going south for the winter, and I am not sure we'll see her again until Season 4.
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