The recipe for this potion can be found inside Daemonheim while Dungeoneering. After finding the recipe, bring it to Lady Meilyr and pay 400,000 coins to permanently unlock the ability to make extreme warmaster. A dose of extreme warmaster boosts the five combat skills by 15% of their level, plus 3. This is very similar to overload, except the boosts for extreme warmaster's potion are like regular extremes. They do not re-boost every 15 seconds.