Teamfighting:

In team fights you want to do maximum damage to the enemy team WITHOUT dying as you are very important to your team and a necessity to win fights. In fights brand is very good at peeling and keeping your AD Carry alive. You can easily stun an enemy that attempts to target your ADC and burst them down without much of a problem. In fights make sure to R(Ultimate) into the the enemy team to deal a lot of damage and most likely apply your passive on the enemy team. With the item Rylai's Crystal Sceptor you can keep the enemy team slowed most of the fight, giving your team an advantage. Using your full combo on the enemy team will chunk the entire enemy team's health allowing the rest of your team to clean up.

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Item Path:

With brand you want to build more of a Healthy/Ap build which gives you a lot of damage while keeping you alive in fights. Try to build Void Staff when the enemy team begins to build Magic Resist to avoid most of their MR. Also, Rylai's Crystal Scepter is very important on brand for many reasons. 1) You can slow down the enemy making it very easy to therefor land a stun on them. 2) Ulting in team fights will keep them slowed down most of the fight giving your team the advantage. 3) With the slow on Rylai's you can peel for your teammates and kite very well. With your build you also want to build Mana and Cooldown Reduction as you want your stuns on a very low cooldown and without building mana you will run out very quickly and be forced to recall alot.

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Roaming:

When roaming, for example bot lane, you want to ult the ADC and Support when they are clustered together, then use your Q ability on the adc as killing the ADC is your first priority. Once stunned you can use your W then ult or ignite for whatever extra damage you may need. When attempting a roam make sure your lane is pushed out so you dont lose too much farm or a turret. Top lane is a fairly simple roam opportunity as you want to get behind the enemy top laner then land your E > Q combo, then W when stunned. Your top laner should be able to finish the kill of from there, but if this is not possible you can use the rest of your combo with your Ultimate and Ignite.