Thorn Bind Hostage

Put 2 (+1 every 3rd level) thorns on the enemy, which snares the target enemy. When an ally hits an affected enemy a thorn brakes and deals 1d4 damage. If all thorns are broken, the snare effect is removed.
After reaching level 8, you can cast this spell on 2 targets (max. 60 ft between targets), after level 15, you can put it on 3 targets.
After level 10 braking a thorn deals 1d4+2 damage.

snare: affected creature can only move at 50% speed