Decastave

You hold a sliver of wood and cast this spell, and the wood turns into a pole of shimmering magical force. This pole can be used as a quarterstaff and acts as a magical weapon. On a hit, the staff does 2d6 force damage and 1d4 radiant damage. The opponent’s hit point maximum is reduced by an amount equal to the amount of radiant damage taken, and you regain hit points equal to that amount. The reduction lasts until your opponent finishes a short or long rest. The opponent dies if this effect reduces its hit point maximum to 0.