Magic penetration is important on brand because of his passive Ablaze. Ablaze is what triggers all of Brands special abilities on his spells and it also damages the target hitting them for 2% of there health every second for 4 seconds. However ablaze doesn't scale on ability power it will only scale with magic penetration so in order to have it tick harder on them get magic penetration and have fun. Sorcerers boots and Void staff plus your magic pen runes are what you need.

In order to deal the maximum amount of damage you have to use all his abilities as fast as possible starting out with pillar of flame. Using pillar of flame is his main damaging attack with ablaze up on his target so in order to the most possible damage you use conflagration immediately after using pillar so you will already have the dot on them and allow the use of pillars special ability. After you have used pillar and conflagration use sear to stun them this will allow you to use pyroclasm, Brands ult, and do a massive amount of damage. After I go through his rotation of Pillar of Flame, Conflagration, Sear then Pyroclasm I follow up with my ignite so not only do I have my own dot doing damage from my abilities I have ignite ticking on them as well by this time the target should be dead or at 25% with both dots still ticking only thing to do left is auto attack your way up to legendary.

Because you have to be so fast in his rotation do damage, he is largely dependent on cooldown reduction. Brands rotation has to be done very fast it takes about 2 seconds for Pillar of Flame to activate and in that time to do heavy damage you must put Conflagration on them then Sear to stun them and let Pillar of Flame to hit them. So getting blue in a 5v5 is important. Remember to cast Pillar of Flame first then put Conflagration them immediately after then cast Sear after Conflagration following Sear should be your ult Pyroclasm then finally ignite.

I use flash as a way to get to my opponent and burst them down and to also get out of tight situations being able to get in and out is an important part of playing Brand. I use ignite more as an execution if the target hasn't died from my rotation and also as a way to stop people from healing as much like with Xin Shao which in that case ignite would be used first then my rotation begins.

In this build I use 9 Magic pen marks for Brands passive and then you have your choice on the mp5 runes either mp5/per level or straight mp5 it doesn't matter late game because by then you are dependent on cooldown reduction which you get form blue which also gives you mana. As for the ability power you want to be able to hit hard in the beginning so go for ability power glyphs and quints it helps alot early game.

So as for the masteries go in the offensive tree I put one in Summoner's wrath for the 10 ability power when ignite is on cd. I decided to leave one point out in Mental Force and go straight into Sorcery for cd reduction then Arcane Knowledge for that 10% magic pen for Brand's dot. After words I maxed out Havoc to increase the damage being dealt then maxed both Blast and Archmage for that extra ability power. I decided to finish out the offensive tree for the extra damage and then went into the Utility and put one point into Summoner's insight to reduce flashs cd then three points into expand mind for the mana. I then went and maxed out Swiftness for the movement speed because being able to catch our opponents is key. Then finally I put the last point into Transmutation for the spell vamp even though it's not much every bit helps when it comes down to a fight.