While holding this pure concentraition of magic, humming with something that can barely even be considered lightning, but pure plasma fighting and screaming to be released only at your will, you gain a +5 bonus to spell attack rolls and your spell save DC.

In addition you may spend a bonus action to regain a Warlock Spell Slot. You cannot use this feature again until a Long Rest.

Storm's Mastery. Part of the construction of this item bears the blood of a mighty spellcaster, a master of the air and lightning magic. When casting a spell that deals Lightning or Thunder damage, you double the modifiers that you add to any of these spells.

Resonance. You find yourself in a strange situation with this item, as you are attuned to an item forged with your own blood, meaning that whenever you cast a spell using this focus your magic enters a bit of a feedback loop. For every consecutive spell you cast with this focus with a maximum of 6 seconds between, you add +1 to your spell attack and spell save DC. E.g. The first spell you cast in combat will not add a bonus, but if you cast a spell the next turn, you add +1, then the next spell adds an additional +1 to be a +2.

Notes: Bonus: Spell Attacks, Spellcaster with the Pact Magic feature, Buff, Combat