Blast Scepter

From Waterdeep: Dungeon of the Mad Mage, page 310.

Description
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.