This spells, like all the other 118 shadow spells gives you the option just before casting of selecting the number of opponents you'd like the spell to hit.
It can be solo (one person), two, three or four.
The damage is divided however.
Try using the spell again with more than one enemies in battle and note the selection process.
Henchmen are the only ones that may use the Shadow Spell and opted not to have the damage divided.
