Double Punch (1･2パンチ 1 2 Panchi?, lit. "1-2 Punch") is a technique used by Knuckles the Echidna. It first appeared in Sonic Advance 2 and later in Sonic Advance 3. It is basic jabs Knuckles gives to his enemies, and a variant of the Punch Attack.
The Double Punch is similar in performance to the Punch Attack, but rather than a three-hit combo, Knuckles only delivers a one-two jab with his left fist and then right fist to the foes in front of him. Also in gameplay, instead of the player having to press a button in succession to execute all three hits like in the Punch Attack, the player only has to press a button once perform the full Double Punch combo.
Sonic Advance 2
The Double Punch first appeared in Sonic Advance 2 where Knuckles can only perform it when in movement. To perform the Double Punch in gameplay, the player has to press while Knuckles is running and he will use it in front of him.
Sonic Advance 3
The Double Punch returned in Sonic Advance 3 where it is one of the moves Knuckles can perform only when he has Sonic the Hedgehog or Cream the Rabbit as his partner. The performance and controls of the Double Punch remain the same, but here Knuckles can only perform the Double Punch while standing still, and trying to perform while moving it will cause Knuckles to stop.
When using the Spiral Attack, Knuckles will launch himself spinning through the air for a short time while keeping his fists in front. This increases Knuckles' attack range, and the force from the speed will engulf his fists in fire. Foremost however, the Spiral Attack allows Knuckles to maintain the speed he is running at and remain in Boost Mode, unlike the normal Double Punch which would make Knuckles slow down.
To perform the Spiral Attack in gameplay, the player must use the Double Punch while in Boost Mode. The resulting speed from the Boost Mode will then transform the Double Punch into the Spiral Attack.
A variation of this move is also used by Knuckles in Sonic Adventure 2 when the third Punch Attack combo is performed at high speeds, where Knuckles will launch himself spinning horizontally, instead of doing an uppercut.