"Incredible, how did you make your clothes grow?"
It is quite likely that any Namekian is capable of initiating this transformation, provided that they know how, as both Lord Slug and Piccolo are capable of transforming in this way. According to Daizenshuu 7, the user grows in height by concentrating the nerves throughout their entire body, invigorating their cells, however, the transformation is quite painful due to the excessive additions to the user's body. According to Goku, this state does not actually increase the user's power level, though it does make them heavier and more durable without impacting their speed, increases physical strength, and also gives their physical blows much greater offensive power.
King Piccolo is very tall for a Namekian (suggesting that he spends most of his time in the Great Namek state) and he can further increase his size, as displayed when becoming enraged after Goku kneed him in the face with a boost from his Power Pole. During this, King Piccolo's strength and power are increased, but he is still unable to destroy Goku. King Piccolo continues to use his Great Namek state while fighting Goku, though he is still defeated by the young Saiyan.
Piccolo transforms like this once in the manga and twice in the anime. He transforms during his fight with Goku in the Piccolo Jr. Saga, and then grows even bigger, but found this form to be ultimately ineffective against Goku (in both the manga and anime), his further size increase is referred to as Super Giant-Form.
In the anime only, Piccolo uses the technique a second time, growing slightly, to equal the size of Garlic Jr. in his Super form. In addition to successfully matching the empowered foe, this technique proved to be very effective against Super Garlic Jr. as due to having proportionally increased his anatomy rather than mostly expanding his muscles, Piccolo's speed and agility remains unaffected. He even goes on to tell Garlic Jr. that "You can't sacrifice speed for power, not against me." This came from the fact that Garlic Jr. in his Super form is mostly an engorged mass of a muscle, inhibiting his movements and by extension slowing him down.
Lord Slug transforms into a Great Namek in the movie Dragon Ball Z: Lord Slug, after Goku attacked him using his "Super Saiyan" power. Despite Goku stating during his fight with Piccolo in Dragon Ball, that the form does not increase power, Slug believes that with this state Goku will be unable to hurt him (even after seeing his False Super Saiyan power). Slug even goes so far as to claim that the size change is his 'true' form.
Video game appearances
Piccolo takes this form in a cutscene in Dragon Ball Z: Super Gokuden: Kakusei-Hen. Lord Slug is playable in this form in the Budokai Tenkaichi series. Slug, Ma Junior and King Piccolo appear as playable characters in this form in Dragon Ball Heroes. Piccolo, as well as King Piccolo, use it during one of their combos in Super Dragon Ball Z.
Namekians are able to perform this transformation in the computer game Dragon Ball Online; their giant form transformation is called Great Namek in this game. In-game this form is equivalent in power to Super Saiyan and Pure Majin.
In Dragon Ball: Xenoverse and its sequel Namekians can be customized to be far taller than the other races.
"Namekians can use the "Became Giant" Awoken Skill, allowing them to use powerful, long-reaching attacks that affect a wide area. A character under the effects of Become Giant cannot be staggered by enemy attacks, but their stamina will gradually deplete over time. Sustaining and attack will also drain stamina. once stamina has reduced to zero, the Awoken Skill will end and the character will enter guard break status. Basic controls are mostly the same while under the effects of Become Giant, but some actions may change or become unavailable. Become Giant cannot be used in all locations. When using Become Giant, the command you input will determine the path of your Mouth Cannon, so consider your foe's position when deciding which command to use. Be aware that you will be vulnerable to attacks from behind during this move."
— Dragon Ball Xenoverse 2 Tutorial Description
In Dragon Ball Xenoverse 2, it appears as an exclusive Awoken Skill transformation for Namekian characters under the name Become Giant. To obtain this form, the Future Warrior (Xenoverse 2) must visit the Guru's House time rift anomaly and assist Nail in protecting the Namekian Dragon Balls from the Frieza Force. Eventually, Piccolo will appear after having sensed the Warrior's Ki and after thanking them for protecting Planet Namek, he tells them that they have untapped strength hidden deep within them and suggests speaking to Nail to learn how to unlock it. Nail reveals he was aware of Piccolo's presence and the Warrior hidden power. He comments that with that power the warrior could easily conquer Namek, but has instead saved it from danger more than once. As a debt of gratitude, Nail decides that he will help them tap into this power and suggests the Warrior talk to Dende for advice on how to awaken their full potential. Dende reveals that in order to unlock their full potential the warrior will need to take themself over the edge by fighting one of their own and suggests that the only Namekians who can help with that are Nail and Piccolo. They must then return to Piccolo which will unlock Guru's House Quest: "Namekian Awakening" where they face off against Piccolo and Nail in battle to unleash their full power and the Become Giant Awoken Skill will become available mid-battle. After defeating Piccolo and Nail using the form, Piccolo and Nail will revive and the Warrior must defeat 3 Piccolo clones and Nail using their Become Giant form complete the quest and unlock the Become Giant Awoken Skill permanently. Become Giant form is fueled by Stamina and it puts the Future Warrior in a guard break state that makes them vulnerable when their stamina runs out. Due to the size of this transformation, it is unusable in certain stages such as Frieza's Spaceship. While in the Become Giant form, Ultimate Skills become unavailable and the Future Warrior gains access to four Super Skills:
- Mouth Cannon: mid-range: Fires a mid-range energy sphere from their mouth.
- Mouth Cannon: short-range: Fires a short-range energy sphere from their mouth.
- Mouth Cannon: long-range: Fires a long-range energy sphere from their mouth.
- Evil Roar: Unleashes a roar that produces an Explosive Wave around the user's giant body.
Additionally their throw is changed to Crushing in Hands.
Great Nameks in Xenoverse 2 are shown to be around the same size as Saiyan's in their Great Ape form, thus the form is useful when combating Great Apes, enabling them to go toe-to-toe with Great Apes. Interestingly, despite the Future Warrior having access to this Awoken Skill, neither Piccolo nor Lord Slug can use this form in Xenoverse 2.
- In Dragon Ball Xenoverse 2, the Namekian Future Warrior gains access to their Great Namek form while fighting Nail and Piccolo. Before the quest that unlocks this ability, it is stated by Dende that the warrior must fight against their own kind to awaken this dormant power, implying some warrior-type Namekians (like the 2nd Future Warrior) require the assistance of other Warrior-types to gain access to their Great Namek form.
- Presumably for other Namekians like Piccolo and Lord Slug this ability may be in born or obtained through other means. One possibility is that Super Nameks naturally possess the ability to access this form, as Lord Slug refers to it as his "true" form while Piccolo presumably inherited the ability from his father King Piccolo who may have inherited the ability to access the form from his original Super Namek self, the Nameless Namekian.
- In the case of Guru, Moori in Dragon Ball Online, and even King Piccolo it is possible that their size may be a side effect that results from a combination of age and/or Namekian reproduction (this may especially hold true for King Piccolo and Guru as they are known to have birthed large numbers of children during their lifetimes).