Off the top of my head get free evil smile gif, there is smirk, grimace, sneer and scowl but there are many words you can use it place of evil smile such as
vile, hateful, malicious, venomous, nefarious, loathsome, wrathful and malicious.
His vile smirk, malicious scowl, venomous sneer or wrathful grimace. Could also be hateful smile, loathsome grin or nefarious frown or any combination of words…