In this talk I will describe the construction of the so-called `anti-tempered' Arthur packets for split p-adic groups using the wavefront set. A key ingredient of this construction is a certain geometric invariant extracted from the wavefront set called the canonical unramified class (also known as the canonical unramified wavefront set) which is intimately related to the Langlands parameter of the Aubert-Zelevinsky dual. This talk is based on joint work with Dan Ciubotaru and Lucas Mason-Brown.