Instructions
Concentrate on the archers accompanying the scorpion first. Attempting to kill the scorpion while the archers are still around will end in you taking a frustrating amount of damage from their arrows. Use poison or fire elemental attacks on the archers rather than melee and dodge their attacks carefully. When they are dead, you can concentrate on the scorpion.
Slow down or stop the scorpion's attacks so that you can get close to him. Using ice elemental attacks to slow him works best.
Close with the scorpion and damage him with melee attacks. Be sure to back away quickly when he winds up for an attack -- you should have plenty of time to do so if you've slowed him with elemental attacks.
Repeat steps 2 and 3 until the scorpion is dead.