From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Ryu-ken (龍拳, Ryū-ken; FUNimation "Dragon Fist"), or Ryu-ken Explosion (龍拳 爆発, Ryū-ken Bakuhatsu; FUNimation "Dragon Fist Explosion"), is a rush attack and the only attack Son Goku creates completely by himself.
First, Goku makes a straight fist faced at his opponent. Next, once his fist along with his own body exits the stomach or chest of his opponent, the energy will explode out into the form of an enormous golden Dragon which bears a great resemblance to Shen Long. Finally, it collides into his opponent, possibly destroying it in its path or leaving a gaping hole, hence the name Dragon Fist.
Goku used this attack against Hirudegarn, Super No. 17, Eis Shen Long, and Omega Shen Long, however, it only directly killed Hirudegarn and Eis, although it allowed Goku to win against Super No. 17 by firing a Kamehameha to vaporize the evil Artificial Human afterwards.
Though it is never stated explicitly that Goku invented this move (he was also never seen learning it from anyone), the move's origins appear to hail from the Dragon Ball anime. The execution of the move is virtually identical to the move he used to kill Piccolo Daimao (called Penetrate! in Dragon Ball Z: Budokai Tenkaichi 3) minus the initial Kamehameha. Instead of a golden Dragon, asilhouette of a Great Ape appeared as Goku's inner powers. (Also, Goku's hand is cocked against Piccolo, whereas the Dragon Fist technique has his hand fully stretched out.)
- Super Ryu-ken (超龍拳, Sūpā Ryū-ken; FUNimation "Super Dragon Fist") – An enhanced version of the Dragon Fist, an attack that was developed by Goku as a Super Saiyan 3. It first appeared in Dragon Ball Z: Hyper Dimension as Goku's desperation attack (a secret combo). Goku, as a Super Saiyan, attempted to gather energy for a Genki Dama, but could not fully control it. Instead, he absorbed the massive amount of energy into his body and was covered from head to toe in a blue aura with sparks surrounding him. He then proceeded to throw a punch at the opponent and took the form of a giant golden Dragon, who then devoured the unlucky target and inflicted a massive amount of damage.
- 10x Ryu-ken (十倍 龍拳, Jū-bai Ryū-ken)
- This is the one of the few rush attacks in the Budokai Tenkaichi video game series capable of being executed against giant characters, such as Great Apes and Slugg (in his Giant form) since Goku uses it against Hirudegarn.
- Gogeta is able to use this attack in Dragon Ball Z: Buu's Fury even though he never uses it in Dragon Ball Z: Fusion Reborn or in his Super Saiyan 4 form in Dragon Ball GT. (After all, it is more than likely that he knows all of the moves known by Goku and Vegeta.)
- Goku's usage of the Dragon Fist during the Super 17 Saga may show that it could be a updated version of the Penetrate! technique.
- The Dragon Fist is widely considered by many fans as the second strongest attack Goku has second only to the Universal Genki Dama.
- The Super Dragon Fist reappears in Dragon Ball GT when Goku kills Eis as a Super Saiyan 4. Goku punches through the Evil Dragon, immobilizing him and falling before Goku's feet. Goku then punches Eis in his back, erupting in a brutal explosion with the Super Dragon. This method of the attack is Goku's Ultimate Blast in his Super Saiyan 4 form in Budokai Tenkaichi 3.
- When Goku uses the Dragon Fist in Dragon Ball Z: Burst Limit, Dragon Ball Z: Infinite World, and Dragon Ball Z: Budokai 3, he finishes the attack by using a Kiai.
- When Goku uses this attack in Budokai 3 and Infinite World, he first absorbs a Genki Dama of some type and attacks his opponent with an amazing Dragon Fist, just like in the original game appearance, Hyper Dimension.
- If the defending opponent's gauge is higher than the attacker's gauge when Kid Goku's Super Dragon Fist is executed in Budokai 3, the opponent will dodge the attack and no damage will be done.