If the target has perks that allow attacking with the Dancing Skill, they may still attack (with all the benefits of an All-Out Attack). Otherwise, they'll simply dance for the duration. Either way, they're unable to defend themselves.

The target may still move around, just so long as they're dancing.

Affliction [22] 
    Disadvantage [+15%] 
        Severe Delusion [-15] 
            "I must take an All-Out maneuver to dance each turn!" 
    Malediction (As Regular Spell) [+100%] 
    Based on Activation Roll [+5%] 
    Resisted by Will [+20%] 
    Magical [-10%] 
    Spell Components [-10%] 
        Must say "dance" in Latin 
Level 2 [27] 
    Increase Malediction to Speed/Range table [+50%] 
Level 3 [32] 
    Add Area Effect (2 yard radius) [+50%] 
Level 4-7 [37/42/47/52] 
    Increase Area Effect by 1 step [+50%]