Twin Peaks Mountaineer

If you lack a built-in water walking ability, bring an Elixir of Water Walking before the match starts so you can cross the river quickly on the way to the enemy flag room.

As Alliance, position yourself at the hut on the Horde side where the Berserking power-up spawns, pick it up, then immediately charge across the water or through the tunnel directly into the Horde flag room. As Horde, grab the Berserking buff at the hut on the east side near the river before pushing into the Alliance base. The Berserking buff lasts 60 seconds, giving you enough time to reach the flag room and still grab the Speed buff.

Enter the enemy flag room, pick up the flag, and use crowd control if needed to avoid being slowed or stopped, since having the buff timer wasted by slows will cause the Berserking buff to expire before you complete the achievement.

As Alliance carrying the Horde flag, exit through the southeastern-most entrance of the Horde flag room to grab the Speed buff. As Horde carrying the Alliance flag, the Speed power-up is just outside the Alliance base on the side farther from the Horde base — on the left if you are going up the ramp, or the right if going down the ramp.

With both the Berserking buff and the Speed buff active while holding the flag, immediately use your /roar emote to complete the achievement — you have ample remaining buff time to type or trigger the emote before either buff expires.