Mag Mell's Rose is the first spell in the spell list. This achievement is easiest done with the spell at level 3 but is possible with level 1 or 2. To do this you'll need to round up five or more enemies, either low on health or weak Homunculi. Once you have five weak enemies in a small group, hold to lock on to one of them and cast the spell. With luck all five of the enemies will get grabbed by the spell and a finisher will trigger. Press when prompted to complete the finisher and get your achievement.