Equipped creature gets +1/+1 for each charge counter on this Equipment.
Whenever equipped creature deals combat damage, put a charge counter on this Equipment.
Equip

(

: Attach to target creature you control. Equip only as a sorcery. This card enters unattached and stays on the battlefield if the creature leaves.)
The counters stay on Banshee's Blade even if it becomes unattached, or moves from one creature to another.