Common Misconceptions About Items - Void Staff vs. Abyssal Scepter

Today will be a rather brief article about casters. The main theme will be magic penetration, which will be abbreviated from here on out as MPen.

With the introduction of Rabadon’s Deathcap, it’s plausible for casters to reach obscene amounts of ability power now, exceeding 500 if a caster is fed (and he won’t even need Mejai’s Soulstealer!). If you see an 800AP LeBlanc run up to your, what’s your first thought? I’m going to have to go with “Oh, shit.”

Yet let’s say that she’s got a Rabadon’s Deathcap and multiple Archangel’s Staves. With all that AP, she’s still only got around 30 magic penetration from her boots and runes – less if she doesn’t have these.

Whenever a person sees that the majority of the damage they took was from a caster, especially burst casters like Annie, Ryze, or Veigar, they go out and buy magic resist items. Regardless of whether you’re a tank or a carry, a good player will adapt his build to counter his enemies. Say you get the most logical choice – a Banshee’s Veil. That’s 50 magic resist right there (I won’t even talk about the bubble).Say you play a typical 30 magic resist squsihy champion. Against a mage with typical 30 magic pen, you have 0 MR and are now taking the full brunt of their abilities. Yet with one Banshee’s Veil, that 50 magic resist negates a good 33% of their damage. Buy an Abyssal Scepter after that and half of their magic damage is down the drain.

What can we conclude from this? Against any good team, your role as a caster becomes less effective based on how much magic resist your enemies have. Thus purely stacking AP is [b]not an option[/b] in any game with relatively skilled players. MPen becomes absolutely essential at this point.
There are five items in the game that either give magic penetration or reduce magic resist – Sorcerer’s Shoes, Haunting Guise, Malady, Void Staff, and Abyssal Scepter. We’ll rune out Malady because it’s not common on most casters, and we’ll rule out Haunting Guise because it’s an item you typically sell towards late-game. Sorcerer’s Shoes will also be ruled out because you should almost always be getting it whenever you play a caster, except in scenarios that will be explained later.

This brings us to the main issue of the day – Void Staff vs. Abyssal Scepter. Let’s go over some stats, shall we?
Void Staff
-2295 gold
-recipe: Blasting Wand, Amplifying Tome

-UNIQUE Passive: 40% Magic Penetration

Abyssal Scepter
-2650 gold
-Recipe: Blasting Wand, Negatron Cloak
-+57 Magic Resist
-UNIQUE Passive: Reduces the magic resistance of all nearby enemies by 20

At a first look, Void Staff seems like a better item. More magic penetration and a smaller cost – it seems like you should only buy Abyssal Scepter when either the enemy team is magic-damage heavy or your own team is magic-damage heavy.

But this isn’t true. Let’s do some calculations. The following calculations assume you’re running 9 MPen Marks, Sorcerer’s Shoes, and the Archaic Knowledge mastery.

Given the existing equipment, you have 28.55 magic penetration and an additional 15% MPen. Remember that magic resist calculations are calculated in the following order:

Percent reduction
Flat reduction
Flat penetration
Percent penetration

Meaning that against a 100 MR target, you’ll first penetrate through 28.55 MR, then an additional 15% of the remaining 71.45 MR, for a total of 29.36 effective magic penetration.

Now Abyssal Scepter gives us a flat 20 magic resist reduction, meaning that it is applied before both your flat MPen and percent MPen. Let’s completely skip the fact that it gives AoE MR reduction, and that it gives you MR, and that it’s slightly more expensive. For now, we’ll only be considering the change in magic resist regarding one enemy opponent.

Against a typical squishy that gets a Banshee’s Veil, they’ll probably have around 80 magic resist. Let’s take the case where you have Abyssal Scepter first. As soon as you get within range of them, Scepter procs its effect and their MR drops down to 60. Then your flat MPen comes in and reduces that 60 down to 61.45. Finally, the remaining 15% from Archaic mastery comes in, bringing their final magic resist down to a meager 26.73. That’s quite substantial.

Now let’s say you have a Void Staff instead. First, the flat MPen from boots and runes kicks in, reducing 80 down to 51.45. After the percent MPen from masteries and Void Staff is accounted for, they have an effective 26.24 magic resist.

(Note that for these calculations I assumed multiplicative percent magic penetration instead of additive – it only amounts to a difference of about 3 MR in either case.)

Now wait a minute. We’ve got around the same total magic resist for both targets. Sure, Void Staff costs slightly less. But what are we missing out on?

Abyssal Scepter gives you 57 magic resist. FIFTY-SEVEN MAGIC RESIST. against any magic damage, you’re suddenly a lot beefier, and you didn’t even need to buy a defensive item like a Banshee’s Veil. In addition, Scepter gives reduced magic resistance in an aura to all nearby enemies, not just the one you’re targeting. That means that on a magic-damage heavy team, you’re greatly helping out your teammates who haven’t got sufficient magic penetration. To me, those bonuses are well worth 400 gold or so, since you're getting roughly the same magic penetration against a slightly bulky enemy (we're maybe talking a mage that gets a Banshee's Veil for defense).

If you really want to do actual calculations, consider that Abyssal Scepter gives 20 flat MR reduction. We need to calculate when the 40% penetration from Void Staff starts to beat Scepter.

Working backwards, we have 20/(0.4)=50

My math isn’t perfect here, as there are minor percentile errors – but these prove to be negligible. There’s a reasonable level of leeway where I would gladly trade 5-10 additional magic penetration from Void Staff in exchange for the bonuses that Scepter gives me.

In short, unless all your enemies have around 100 or more magic resist, you really don’t need to buy Void Staff. This is, again, assuming that you go with MPen boots and marks, and take Archaic Knowledge. Abyssal Scepter proves to be better in almost all cases where your priority targets have less than 100 MR.

Obviously, use prudence with these decisions. Many casters sometimes forgo the standard Sorcerer’s Shoes in favor of Mercury’s Treads or Ionian Boots of Lucidity – in this case, the calculations are no longer as relevant and you may find that Void Staff is efficient at a lower base MR.

Regardless, what we see here is that Abyssal Scepter is almost always more effective against squishy targets compared to Void Staff with the standard mage rune/mastery layout. Magic penetration is an essential part of playing a caster, so when you’re deciding between these two items next time, think of this article to tell you what to play.

I hope this helped you with another item discrepancy that you may have had. Next week... I’m not quite sure what I’ll be going over, actually. I’m welcome for suggestions. Anyway, thanks for reading, and I’ll see you guys next time.