Technomancer Staff

Weapon (quarterstaff), rare (requires attunement)
  A focus for pliers of electrical currents and lightning-based magic, this staff represents the evolution of wizardcraft and artifice. While old-fashioned mages potter about with candles and arcane runes, the new blood embraces technology. This staff contains the latest in magic energy catalysts, allowing it to recycle and redirect residual magical energy.
  You gain a + 1 bonus to attack and damage rolls made with this magic weapon. While holding this weapon, whenever you cast a spell that deals lightning damage, roll a d6. You gain a damage bonus to one roll of the spell equal to the number rolled.
  Lightning Rod. When you or a creature within 20 feet of you is damaged by a lightning spell or effect, you can use your reaction to absorb part of the damage dealt to that creature. The damage is reduced by an amount equal to 1d10 + your proficiency bonus.
  Residual Charge. After you cast a spell that deals lightning damage, or use the ‘Lightning Rod’ feature, purple crackling energy gathers at the tip of this quarterstaff. The next time you hit with a melee attack using the staff you deal an additional 1d6 lightning damage. After you hit with a melee attack, or after 1 minute (whichever comes first), the staff loses this charge.
  Very rare variant: Increase the attack and damage bonus to + 2; increase ‘Lightning Rod’ to 2d10 + your proficiency bonus, and increase the d6s to d8s.
  Legendary variant: Increase the attack and damage bonus to + 3; increase ‘Lightning Rod’ to 4d10 + your proficiency bonus, and increase the d6s to d10s.