Source - Waterdeep: Dungeon of the Mad Mage

Rod, Very Rare (requires attunement)

The Blast Scepter can be used as an arcane focus.

Whoever is attuned to the Blast Scepter gains resistance to fire and lightning damage and can, as an action, use it to cast Thunderwave as a 4th level spell (save DC 16) without expending a spell slot.