I would also like to add to the MBR on Warmog argument.
1.) Saying MBR makes Warmog useless is like saying LW/VS makes resistance useless.
2.) ALL characters have a MINIMUM of natural 30 magic resist even at level 1 and some characters ranges up to 50+.
3.) Most people who get MBR are not those who get magic pen.
4.) 30 MR is 23% reduction. 50MR is a 33% reduction. The effect of BR is only doing 2.5%-3% HP per hit. This assumes the bare minimum MR. This isn't even counting the 6 you get from masteries in the defensive tree, not counting the 4% reduction in damage in the defense tree, not counting the MR glyphs tanks get.
5.) If you react to Warmogs with about 3000gold item, a simple 700ish gold item can negate almost the majority of the effect stacking with your base MR.
This is taken from another post
"How, exactly, does having a Warmog's Armor mean that you will die any faster to Madred's Bloodrazor than if you don't have it?
I can understand that statement if and only if you assume that the person with the Warmog's Armor doesn't have (or intend to get) Magic Resistance to offset the Madred's Bloodrazor, but otherwise, I'm obviously missing the logic behind this seemingly universal assumption.
Now, based on the math I've learned in my lifetime, I can surmise that 4% is 1/25th of 100%. That means it would take (without additional damage being calculated) 25 hits to kill a champion.
How does this change based on your total health?
4% of 2000 is 1/25th of 2000.
4% of 3000 is 1/25th of 3000.
4% of 9,718,972 is 1/25th of 9,718,972.
So, whether you have 2000 HP or 3000 HP, or even 19,000,000 HP, Madred's Bloodrazor will always chip away 1/25th of your HP with its on-hit effect.
According to my calculations, then, the only factor that will increase the potency of Madred's Bloodrazor is Attack Speed (on the champ with the Bloodrazor) and MgPen vs. MgRes.
Assuming that much is correct, the only valid argument to be made is that Tristana will, if you don't purchase a Warmog's, simply not buy Madred's Bloodrazor because you're easy enough to kill without it. If you have high HP, Madred's Bloodrazor becomes a necessity. If you have low HP and only stack Armor/MR, she would instead pick up a Last Whisper, which costs significantly less gold, and own you in the face anyway.
Assuming again that my math is correct, having more HP (in conjunction with the Armor and/or MR that you stack thereafter) would mean that, even though you're losing 1/25th of your HP per hit from Madred's Bloodrazor, all other incoming damage has a significantly smaller impact on your total HP percentage.
So, someone please explain to me why Madred's Bloodrazor kills you faster if you get a Warmog's Armor if there is a reason aside from, "Because you didn't buy Magic Resist, which would have lowered the damage from Madred's Bloodrazor," or, "Because they wouldn't have bought Madred's Bloodrazor if you didn't buy Warmog's Armor."
If there is no reason aside from those two, then I feel I can do little more than state, once again, that buying Warmog's Armor does not mean that you will not have high resistances. In fact, it's the very opposite. Buying Warmog's Armor serves the purpose of securing a large HP bar so that you can focus - thereafter - on nothing but increasing your Armor, MR and overall utility."
Bloodrazor is just as deadly on tanks with or without Warmogs. The mitigation is still applied to both the actual physical damage and the effect of bloodrazor. The 1/25th is before ANY mitigation. Now the damage that isn't part of the 4% is effected by mitigation as well. Having higher EHP means that the damage that isn't by bloodrazor is actually doing LESS damage to your overall EHP.