From Dragon Quest Wiki
Quest #109 - "Elementary Training"
Location Alltrades Abbey
Availability After defeating Master of Nu'un
Requested by Windy
Fulfilled to Windy
Reward Armamentalist class become available.
Detail Windy at Alltrades Abbey says you must use the Fource of Mother Nature if you want to join the great fellowship of Armamentalists. He wants you to erect a Wizard Ward before defeating two Metal slimes in battle.
Hint for solution Equip your Mage party member with Poison needle. Try weakening the Metal slime with a Metal Slash, a sword skill, after you have casted Wizard ward. Note that the mage who cast Wizard ward must be the one to defeat the Slime.
Repeatable No