Butterfly Knife | Doppler Phase 4 (BFK P4) was added to the game on March 15, 2017, alongside the "Take a trip to the Canals" update. The skin is available in cases "Spectrum" and "Spectrum 2".
The blade of the knife is painted with metallic paints and adorned with a pattern of translucent wavy lines resembling smoke. The color scheme of the skin includes various shades of blue, brown and black creating gradient transitions. The handle is unpainted and complemented with blue inserts.
Float Value of the skin ranges from 0.00 to 0.08, which makes Butterfly Knife | Doppler Phase 4 available only in Factory New and Minimal Wear condition. At levels of wear close to the maximum, the knife has noticeable scratches and abrasions located along the cutting edge.
The pattern index affects the ratio of colors as well as the location of blue, brown and black areas. Pattern variations with a predominance of blue on the play side of the blade are titled “BTA Blue”. Knives with only blue color on the blade resemble Butterfly Knife | Doppler Sapphire and are titled “Max Blue”.
The quality of Butterfly Knife | Doppler Phase 4 is Covert. The skin has a StatTrak option and is close to phases 1 and 3 in terms of rarity. The skin belongs to the "Butterfly Knife | Doppler" series.
“Doppler Phase 2” is one of the most popular skins for M9 Bayonet. The skin has a very large number of fans and is considered to be more valuable than phases 1, 3 or 4.