Adder Shillelagh

The wood of a club or quarterstaff you are holding is imbued with nature's power. For the duration, you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks using that weapon, and the weapon's damage die becomes a d8. The weapon also becomes magical, if it isn't already. The spell ends if you cast it again or if you let go of the weapon.

You can use a bonus action to speak the staff's command word and make the head of the staff become that of an animate poisonous snake for 1 minute. By using another bonus action to speak the command word again, you return the staff to its normal inanimate form.

You can make a melee attack using the snake head, which has a reach of 5 feet. Your proficiency bonus applies to the attack roll. On a hit, the target must succeed on a DC 15 Constitution saving throw or take 3d6 poison damage.

The snake head can be attacked while it is animate. It has an Armor Class of 15 and 20 hit points. If the head drops to 0 hit points, the staff is destroyed. As long as it's not destroyed, the staff regains all lost hit points when it reverts to its animate form.