The most recognizable feature of this event was changing regular sprites of Pokémon (static raster graphics of 3D models) into 8-bit sprites known from original Pokémon games. Moreover, there was increased spawn rate of Murkrow during the event, and shiny variant of it released to be caught in the wild.
Murkrow would have increased spawn rates in the wild (and from Incense, Lure Module).
Banners for in-game news changed during the event, portraying the Pokémon as 8-bit sprites.
Pokémon 8-bit sprites