The ability to transform into a state beyond Super Form where one's powers and potential are strengthened to a higher degree.
The user can transform into a state beyond Super Form that greatly increases the user's power, giving them an even larger increase in strength, speed, and skills, as well as gaining new abilities and having their previous ones strengthened to an even higher echelon of power.
The Heisei era Kamen Riders (Kamen Rider Series); via power up items
The Super Ranger forms (Super Sentai); via upgrades, usually reserved for Red Rangers but some can be used by the full team.
Heisei era Ultramen (Ultraman series); via fusing with one or multiple Ultramen or gaining extra power from another source.
R1 Max and Fire-1 X (Tomica Hero Series); activated via the Max Commander and the X-Basher devices
By using his Alter power at it's maximum, Kazuma (s-CRY-ed) becomes harmonized with his Shell Bullet and is able to access his strongest form, Proud Fist.
Much like Kazuma, Ryūhō (s-CRY-ed) can use his Alter power at it's maximum, becoming harmonzied with his Zetsuei, allowing him to access his Zetsuei Touryudan form.
Hyper Sonic (Sonic the Hedgehog series) is a transformation that Sonic can achieve when he collects all seven Super Emeralds. In his hyper form, possesses all of the abilities of his super form at a much greater level.
Son Gohan (Dragon Ball series) was the first to achieve the Super Saiyan 2 transformation. In this form, Saiyans surpass the power of an Ascended Super Saiyan and an Ultra Super Saiyan, allowing them to increase their strength while maintaining their speed.
Son Goku (Dragon Ball series) was the first to achieve the Super Saiyan 3 transformation. In this form, Saiyans surpass the power of a Super Saiyan 2, using power extracted from every drop of their blood.
Son Goku and Vegeta (Dragon Ball GT) are the only known Saiyans to have achieved the Super Saiyan 4 transformation. In this form, Saiyans are at their strongest, with all of their power drawn out to its utmost limits.
In his intense rage during the conflict with Goku Black and Future Zamasu, Future Trunks (Dragon Ball Super) took on a new, immensely powerful Super Saiyan Anger form.
Caulifla (Dragon Ball Super) became the first female Saiyan to transform into a Super Saiyan 2.
Kale (Dragon Ball Super) became the first female Saiyan to access the Legendary Super Saiyan transformation.
Kale's (Dragon Ball Super) Legendary Super Saiyan 2 form not only makes her stronger than the initial one, but also allows her to retain full control over herself.
During his participation in the Tournament of Power, Cabba (Dragon Ball Super) obtained the Super Saiyan 2 transformation.
Given that her fusees, Caulifla and Kale, posses the Super Saiyan 2 and True Legendary Super Saiyan transformation, Kefla (Dragon Ball Super) is able to incorporate both elements of the forms into her Strengthened Super Saiyan 2 form.
Type Tridoron is Kamen Rider Drive's ultimate form. It is a fusion of Shinnousuke, the Drive Driver, and all 26 Shift Cars with his car Tridoron acting as the armor.
By "sundipping," Superman (DC Comics) immerses himself in the sun and absorbs massive amounts of solar energy, greatly powering him up.
Ultraman Exceed X (Ultraman X)
Using the Hyper Share Crystal Neptune along with the 3 other Goddesses Noire, Blanc and Vert (Hyperdimension Neptunia series) gained access to a transformation called Next Form that vastly surpasses their previous Hard Drive Divinity transformation.
Shishi Red's ultimate form, Shishi Red Orion (Kyuranger) is accessed through the use of the Saiko Kyutama, allowing him to combine the powers of all 12 Kyurangers along with the great power of the Orion System.
Monkey D. Luffy's (One Piece) Gear Fourth - Bounceman, his default transformation...
...and Gear Fourth: Tankman, which focuses on defense...
...and Gear Fourth: Snakeman, which focuses on offense and speed over defense.