Hussnasty Mode is an art style used in Homestuck. It is more realistic than Hero Mode, and unlike Hero Mode and the normal character sprites, characters are depicted with noses and ears in this style, as well as irises if zoomed in close enough. It first before Rose had her first conversation with Eridan.
The name originated on Andrew's old formspring account, where he jokinglythat in the future he wants the style of his work to be referred to as "Hussnasty" in the same way that "Shakespearean" is used to describe things like Shakespeare's work. The word was applied to this art style because it more closely resembles Hussie's style in his older more detailed works such as "Whistles."
The term is sometimes mistakingly used for contributions of the Art Team since several of them work in a style featuring details such as noses.