Double Boost (W. (ダブル) ブースト,W. (Daburu) Būsuto?), also known as the W. Boost, is a move that appears in Sonic Forces. It is a collaboration technique between Sonic the Hedgehog and the Avatar where they combine their strength to perform an augmented Boost.
When performing the Double Boost, Sonic the Hedgehog and the Avatar focus their power into one of their hands and then high-five each other with them. The two then do a midair Spin Jump before dashing away side by side, each one performing a Boost that augment the other, thus greatly amplifying their combined speed. In fact, the speed this move generates at maximum power is great enough to allow one to breach even dimensional barriers, like those of Null Space.
In gameplay, the Double Boost appears exclusively in Tag stages, and it is triggered when a Real-Time Interaction is initiated, in which the player must tap // enough times within a few seconds. If performed correctly, Sonic and the Avatar will boost away like when performing the Boost, but at far greater speeds, while a short version of the song "Fist Bump" replaces the background music. In some cases, "Fist Bump" replaces the background music in its entirety. The Double Boost ends when the Boost Gauge runs out, but it can be refilled by destroying enemies and collecting Rings. If the Real-Time Interaction is not done correctly, Sonic and the Avatar will stumble for a second before the aforementioned Boost is performed along with the vocals being cut off.
The Double Boost is required for the Null Space stage to escape from the titular trap that Sonic and the Avatar were put into by Dr. Eggman as well as the ending of Final Judgement, where the Avatar and Sonic need to escape from the doomed fortress after destroying the Phantom Ruby backup generator. In addition, using the Double Boost is needed to deliver the final blow to both Metal Sonic and the final Infinite fight during their respective boss battles.
The Double Boost is known in Japan as "W. Boost", likely due to the prounciation of "double" in Japanese (ダブル,Daburu?) sounding similar to the letter "W".
During the first Double Boost section in Arsenal Pyramid, if the player runs out of Double Boost (by actively dodging the enemies you're racing towards), the player will continue running at the same speed, just without the boost effect. Additionally, they will not collide into enemies; instead, they will phase past them.
In the PC version of Sonic Forces, when playing with a keyboard, the button prompt has the word "Boost" on it. When playing with a controller, the button prompt shows which button the player has set as the Boost button.
In promotional trailers, the red-starred Resistance logo is shown in place in the button prompt.
The player cannot use the Double Boost as Super Sonic as it will instead force Sonic out of the transformation in order to use the move.