Does magic penetration affect Zyras Plant Pets?

Also, do items like sorcerers shoes benefit people like Swain an Cassi (small yet stacked damage over time) more than Leblanc or Viegar(Large chunks of burst damage?)? Do the multi-hit spells go through a resistance check each time they go off?

Hey Kersallus

Also it does effect Zyra's plants, because that is a part of Zyra's damage!

Magic penetration works all the same with spells, even with the DOT spells (Damage over time). This is because each tick to the opponent is a new set of damage.

I could go into more details if you wish but I think this answers your questions.

Happy Summoning

~Nidilen

Go for more details please

I also want to know if im teaching right here, I told my friend that akali can use mpen with 3 of 4 spells and gives flat penetration, and she asked about getting sorc boots and haunting guise, and I told her they stack (Am I right?), and as far as I read on guides from everywhere, they suggest not combining flat magic penetration with percentual magic penetration, because they do not combine well (idk why)

So each of the 3 hits of Swains Q spell faces an Mres check?

Here it comes all about Mres: http://leagueoflegends.wikia.com/wiki/Magic_penetration
I need to check the internet before posting I guess.

About the Swains Q, ill copy and paste what wiki said about it:

- Decrepify is a targeted tethered damage over time ability that releases Swain's raven at his current location, tethering to a target enemy unit for up to 3 seconds. While the tether holds, the target takes magic damage every half second and is slowed.
- Decrepify procs spell vamp and Rylai's slow similarly with all damage over time spells and abilities with diminished effect.
- Decrepify pops spell shield.
- Decrepify will damage Black Shield and the slow is negated.
- Decrepify has no cast time.
- Swain may act freely while Decrepify is active.
- Decrepify's effects persist even if Swain dies.
- Decrepify's slow and damage are interrupted as soon as the tether breaks.

So, his Q is magic and benefits of AP, and MRed (the ticks of the DoT too)

Blah, I think I'm not being clear. xD

Say Swains Q does 300 damage, and the target has 50 magic resist. Do they take 250 damage overall(m resist applied to total), or 150? (m resist applied for each tick) Also, does 20 spell penetration make the aforementioned numbers 270 for the first, and 210 for the second (spell pen applied for each tick)?

That's not how MR works. MR reduces damage by a percent. 100 MR makes Magic Damage deal 50% as much, 200 makes it deal 33.333% as much, and 300 makes it deal 25% as much.
Swain's Q does 300 damage. If they have 0 MR, each tick (there are 6, once every 1/2 second) will deal 50 damage, for 300 total damage.
If they have 100 MR, each tick will deal 25 damage, for 150 total damage.
If you use Swain's E to deal 300 damage, all at once, and they have 0 MR, they will take 300 damage immediately. If they have 100 MR, they will take 150 damage immediately. (When I say immediately, I mean after the short delay on the W, they take all the damage at once)

Also, as you don't have preconceptions, so you'll be more willing to listen-
Armor and MR do NOT have diminishing returns. What happens, is that as you get more MR/Armor, HP becomes more valuable. The Armor and MR are always worth the same amount, regardless of how much you already have (unless the enemy is reducing/penetrating through all of it if you have a very small amount, but that's almost never going to happen), whereas HP gets more valuable as you level up. Therefore, assuming you will only be taking one type of damage, Armor/MR is more valuable at first, and HP will eventually become worth more. Due to the cost of the stats, though, getting HP if you are at 2K already, is only worth it if you already have 70-ish in both resistances.
All assumptions regarding buying resistance versus HP assumes you take exactly even Magic and physical damage. You usually take more physical damage, so armor is generally worth more than MR, and HP versus resistance value is usually rather complex, so you have to eyeball it.
Also, True Damage ignores all resistance, so a team with Darius and Irelia makes HP more valuable than usual.

Edit: Also, the effective health formula, which determines what percent of damage the resistance blocks, is 100/(100+X), where X is the relevant resistance.

Hello Again

Well I guess its my turn to explain a little further! (Most likely last post for about 3-5 hours)

Okay so lets start at the begining! (Note: This applies for this season (season 2) because season 3 will have different rules!)

So lets say you opponent has 100 Magic Resist, and you have 10 flat magic penetration and 10% Magic penetration

First we will figure out how much your spells would be reduced without any penetration at all!

Magic Resist:

Damage Multiplier = 100/(100+Magic Resist)
So if the opponent had 100 Magic Resist
100/(100+100) = 0.5
0.5 is going to be the damage multiplier for that target.

Lets say your spell would orignally do 100 damage to the target (flat damage).

You would take the damage multiplier (aka 0.5) and times it by the damage you were going to do.

0.5*100 = 50 damage done by that spell.

But now going into magic penetration (Flat)

Lets use the situation from above ^^^

Lets say that your opponent has 100 Magic resist and you have 10 magic pen reduction
Their Magic resist would become 90 Magic resist with your spells and the damage multiplier would be:
100/(100+90)= 0.526
SO if you had a spell that deals 100 damage you would take 100*damage multiplier (.526)
and your damage to the target would be 52.6 (53).

Magic Penetration %
Once again lets say your opponent has 100 Magic Resist and you have 20% magic penetration
you would take 100 - 1/(magic penetration)
In this situation it would be 100 - 20 = 80
So then the damage multiplier would be 100/(100+80) = 0.556
So if you had 100 damage coming from a spell the damage you would give would be 55.6!

Mixed Penetration
Magic penetration applies first then % based! So lets say once again that your opponent has 100 Magic resist and you have 10 flat magic pen and 20% magic pen.
First
100 - 10 = 90 Magic resist (for the flat)
Then
90*0.8= 72 Magic resist (for %)
Then the damage multiplier would be 100/(100+72) = 0.58
So if you were to do 100 damage with a single spell you would end up doing 58 damage!

So now lets move on to DOT spells, like swain!

Lets use his e ability!

He does that flat amount of damage over 4 seconds, so on each tick, the Magic Penetration is being applied. So lets say swain does 400 damage originally with his e ability (including the flat amount of damage).
Each second he would be dealing 100 damage if there was no Magic resist on the Opponent.

But the enemy has 100 Magic Resist, and swain has 10 flat and 20% magic penetration.
Each tick of damage would do 58 damage because
First
100 - 10 = 90 Magic resist (for the flat)
Then
90*0.8= 72 Magic resist (for %)
Then the damage multiplier would be 100/(100+72) = 0.58

So to answer your question, the Magic penetration is applied on every single instance that Magic damage is applied!

If there is any way I can help you further understand Magic penetration just ask!
~Nidilen