A note, in regards to resistances.

The way resistances work in League of legends, is sort of a "Diminishing returns effect" ... Allow me to try to explain in a simple way.Go into a custom game, and buy 5 Thornmails. You will find that as you get higher armor and higher, the % of damage reduction begins to scale up more and more SLOWLY.Amazing LOL left a comment on how the actual process works and I'll leave a few examples using the same math to show the progression and how it tops out.---It's simple math. Take your armor, for example, and divide it 100 times + your armor, then multiply by 100.Example:I've got 20 armor. So 20 / (100+20) = 0.17 x 100 = 17% reduction.On higher armor values, like... 350: 350 / (100+350) x 100 = 78% reduction.---So, I'll leave some example using that math now, to show the progression and how you get less and less reduction the higher you go.20 / (100+20) = 0.17 x 100 = 17% reduction......20 / (100+20) = 17%(The next 20 armor provides 11% more reduction.)40 / (100+40) = 28%(The next 20 armor provides 9% more reduction.)60 / (100+60) = 37%(The next 20 armor provides 7% more reduction.)80 / (100+80) = 44%(The next 20 armor provides 6% more reduction.)100 / (100+100) = 50%(The next 20 armor provides 4% more reduction.)120 / (100+120) = 54%(The next 20 armor provides 4% more reduction.)140 / (100+140) = 58%(The next 20 armor provides 3% more reduction.)160 / (100+160) = 61%Etc...350 / (100+350) = 78% reduction....So, as we can see quite clearly, you're buying the same amount of armor, and getting less in your % of DMG reduction for each point. =)Because of this, Flat armor or magic pen items in early and mid game are incredibly powerful. They remove the best part of damage reduction, the low numbers give you the highest amount of reduction, and flat pen breaks that early.That's why when you pick up ARP runes and a Brutalizer you deal about the same damage as if you had AD runes and a BF sword to some targets. The amount of armor pen will have you dealing true damage or perhaps if you pen all their armor, even increased damage.Against targets with low resistances, AKA, a carry or something like that, the impact is still substantial in the end game, because you might still be cutting through 1/4-1/2 of their resistances with something like 20-40 ARP. (Most carries won't break 80 resistances.)However, in the same way that flat bonuses have a large effect against carries, their effect gradually over time carries less, and less impact against highly armored and resistant targets.Flat Mpen or flat ArP eventually begin to have their effect reduced, because of the way resistances "Top out" after a certain point.For example, if you have so many resistances, that you've begun to "Top out" already, you're not getting the best returns on your investment... Right?Not necessarily.Most players will run ArP reds and quints on their AD carries, and Mpen or AP on their AP casters and buy sorc boots for the Mpen later.This means that most AD carries and AP carries will have between 20-35ish ARP or Mpen, even at very low levels. Some of it is invisible, you simply have to know it's there.This means, your armor and Magic res is not as high as you think it is. You have to build more to get the full benefit of "The sweet spot" as I call it. You have to build about 20-30 resistances farther at least into the area where you begin to "Top out" and get poor returns on your investment, so that after the opponent's reductions are factored you're still comfortably taking advantage of the high resistances you get early.I judge that area to be around 130-150 resistances or higher. When a champion buys an item like last whisper, you might need to get up to as high as 170 to make up for the difference, or just build a bit more damage so you can kill them or render them unable to sit and attack you, and force them to run.The reason people are not succeeding as tanks with "Tanky DPS" champions, is because they're simply building health and a banshee's veil or two, and calling it a day.But, the amount of resistances they build leave them vulnerable to items like Youmuu's, SotD, Black cleaver, Starks, and others.However, if a player were to build -more- resistances, and -less- damage items, they would get their resistances to start topping out.This would cause the other player's armor pen to only lower them back down to "The sweet spot" of resistances, where every point is still making a large difference, and therefore, your resistances will still be very high.This is the concept behind an Off-Tank, and this is what makes it work.This is why I tell people so often, don't refer to them as the same thing, you're hurting yourselves and the community. A Tanky DPS is a carry with some HP and some minor resistances. You're building damage, and your intent is to carry.An Off-Tank is a tank with some damage. Your intent is to tank, and also mix thing up. Their carry's should never feel safe, and your team should feel confident following you into the fight.Trust me, Last Whisper and Void Staff will help a lot against an Off-Tank, but it's not going to take an Off-Tank out of the game in one item. There is no easy solution to beat a well farmed off-tank, who has planned their resistances and their source of damage well.Also, another thought. People seem to forget that items like Randuin's and Banshee's veil are both great items in regards to stats, but also in regards to their "utility" effects. Randuin's greatest source of damage reduction, is not the 75 armor it provides, but rather the 35% slowing to attack speed and move speed. Banshee's veil protects you from a spell, which in the end game could be up to 500-1000 damage, or a CC that leaves you exposed to tremendous damage.Those effects double as resistances to some extent as well, by protecting you in more ways from the incoming damage. When you finally add all the effects together, the result is quite impressive how difficult you are to kill, and both teams will feel the difference.And all you have to do, is top out your resistances just a little bit, so that you're actually getting the most out of them, and use the utility effects on your items =)