After rigorous training and unlocking the full potential of your Stand, you have achieved the extraordinary ability known as "To Stand Over Heaven." With this upgrade, you can access any canon Stand from the JoJo's Bizarre Adventure universe, with the exceptions of "The World Over Heaven" and "Made in Heaven." Initially, you can switch to any canon Stand, but you are limited to using one Stand at a time.
As you progress and grow in power, you will gain the capability to wield multiple Stands simultaneously. This newfound proficiency allows you to combine a diverse array of Stand abilities, making you a more formidable force on the battlefield. The fusion of different Stand powers grants you unparalleled versatility, enabling you to adapt to any situation and overcome challenges.
However, the ultimate pinnacle of your power lies in mastering Requiem and Stand Combination. With time and experience, you will acquire the ability to access the Requiem form of any Stand you are using temporarily, significantly enhancing its power and capabilities, however, through training you will be able to use the Requiem form of any stand permanently. And through Stand Combination, you can merge multiple Stands into one, amplifying their power and creating an awe-inspiring Stand known as "The One Above Heaven."
Nonetheless, attaining such extraordinary heights comes with great risks. The power of Stand combination is a double-edged sword, and you must tread carefully to prevent being overwhelmed by the sheer force of this amalgamation. While "The One Above Heaven" grants you unparalleled might, it also demands immense control and focus to prevent the power from consuming you. To access "The World Over Heaven" and "Made in Heaven", you will need to undergo a specific rituals or go through intense training to unlock their potential.