You'll need a character of at least level 17, with 9th level spell slots. Octavia or a sorcerer would need to be 18th level or higher, and Tristan, Harrim, a wizard, cleric or druid would need to be 17th level. You'll need to take the feats “Metamagic (Heighten Spell)”, “Metamagic (Empower Spell)”, “Metamagic (Extend Spell)”, “Metamagic (Maximize Spell)”, “Metamagic (Reach Spell)” Most of these feats are questionable and taking all of them is really questionable, so I recommend saving and retraining, then reloading to a good build.
Pick a first level spell, like Snowball, Cause Fear, or Ear-Piercing Scream. Use the metamagic tab in your spellbook to apply all five feats. Save the spell, and prepare it. Rest to restore the slot. Get into combat, and cast the spell to unlock the achievement.