Shakunetsu Hadoken

Shakunetsu Hadoken (灼熱波動拳, Shakunetsu Hadoken, "Scorching Surge Fist") is the name of a special type of Hadoken used by Ryu (as well as his evil side) and Akuma.

Description
Executed by performing a half-circle forward (or backward depending on the character) motion and pressing punch, the Shakunetsu Hadoken is imbued with thermal energy that sets it on fire. In Akuma's variation, he flashes red and charges for a short few seconds before releasing it. The projectile hits 1-3 times, depending on the strength of the punch button.

Although all users can launch a regular Hadoken, this version is usually multi-hitting (allowing it to win projectile wars) and deadly. Any foe hit with this will receive a good amount of damage and stun, and be lit on fire. This projectile is literally a fireball, unlike the normal Hadoken (which is commonly referred to as such).

Ryu
Ryu's version is considerably less damaging than Akuma's, but Ryu does not charge when using it, thus making his version faster to pull off than Akuma's (about the speed of a regular Hadoken charge). From Street Fighter III onwards, his version of the move does not appear directly, instead functioning as his EX Special Hadoken.