Embodiment of Power
The Sith is forced to rely on their potential alone - their strength in the Force and their ability with their lightsaber. The individual is forced to face down their Master or an adversary, they are expected to be able to best the adversary or meet their master on equal ground. The battle takes place anywhere, however a simulation training chamber is the most common place.
Typically it is expected that the apprentice gives into their anger and the dark side during the first attempt. It is almost always guaranteed that the apprentice would fail versus their master, however those that are stronger are expected to meet on equal ground, or best their adversary. While the Embodiment in theory is easy, it is one of the last Embodiments a Sith typically pursues last, once they have gained enough power to stand toe-to-toe with a powerful adversary, which is the entire point of the Embodiment.
Embodiment of Suffering
The Sith is forced to suffer - there is to be a sacrifice to destroy the apprentice and reshape them. The apprentice is to either kill someone they hold dear (or multiple individuals that are either family, lovers, or friends) or to sacrifice flesh, though the sacrifice of flesh is not a missing limb, the sacrifice of flesh is extensive damage to the individual, be it a need for life support or extensive cybernetic implants and replacements for the individual to function or even sacrificing their own will to their master.
Typically this Embodiment is hard on the apprentice, but shows that mercy is out of reach, even with their master and to remind the individuals that relying on the past is a weakness. The suffering should be made to bring the apprentice over the edge of anger and transform the apprentice into something that separates them from other acolytes. The apprentice will more than likely harbor hatred for their master, but it is a lesson to teach the apprentice that weakness must be destroyed and replaced by fury. Those that are incapable of completing this Embodiment are more than likely incapable of advancing forward in the Sith Order.
Embodiment of Tenacity
The Sith is forced to take on a challenge - they are to overcome a challenge that is either provided by their master or by a Kaar. Taking on a mission or a campaign against the Republic is one of the many ways to complete this Embodiment, but not the only way of surpassing it. The master is to decide the apprentices requirement but the tasks usually is intense and requires the apprentice to utilize all their skills to survive the challenge and show their worth as a Sith.
Typically this Embodiment is the most challenging experience an apprentice will go through during their tenure as a Sith apprentice, but it also symbolizes growth. Should the Sith fail the Embodiment, the master is expected to discipline their apprentice and force them to endure another challenge, but each and every challenge is different. An individual could be cast onto a barren planet with nothing but the Force to survive and their skills, or sent into the barren wastes of Korriban to survive for weeks while enduring the chatter of Sith spectres and the beasts of the desert.
Embodiment of Devotion
The Sith is forced to show their devotion - they are expected to show they are willing to serve the Empire and their master. The individual is to empower their master's power structure and the Sphere they represents power structure, therefore strengthening the Empire. Diplomacy is a perfect tool for this Embodiment and having a silver tongue is beneficial to those who seek to gain an ally outside of the Empire - a neutral force, or to influence those within the Republic.
Typically this challenge is spread throughout the apprenticeship and is to ensure their master keeps their life - defending their master's life against would-be assassin's and using diplomacy to gain those who are neutral to the Empire's side, or those who are under no Sphere of Influence to join their master's power structure.
Embodiment of the Dark Side
The Sith is forced to embody the dark side - they are expected to let the dark side encompass their being and show their corruption through their body. The dark side envelops the spirit, forming an aura of malevolence that others can feel; and an individual's irises permanently retain their pigment transformation while the skin pales. The individual is meant to cast aside their attunement to the light side of the Force and face their self-reflection brought on by the Force, a reflection of their spirit.
This Embodiment is the easiest to obtain if they keep down the path of a Sith. The apprentice is to be expected to keep this level of corruption and if they fall to being pure, the consequences will be dire. Self-reflection typically occurs in Force nexuses such as Korriban, the Dark Temple on Dromund Kaas, Vjun and other spots that thrive with the Force, though immersing themselves into the Force can potentially lead to revealing their own reflection. The battle is a battle of wills and to cast aside their reflection symbolizes the final step towards the position of a Sith Master.
This is the final step before a Sith can advance to the rank of Sith Master, completing their training as an apprentice. The Sith kneels before their master and repeats the Sith Code along with their master. Once this is completed the master will christen the Sith with a Sith name that they will use from this moment on, instead of their birth name - marking them as an official Sith among the Empire. The Sith name that is bestowed upon them by the Force isn't always Ancient Sith, but sometimes represents a trait they possessed in their life.
The Sith now serves under their master still, while serving the Kaar of the Sphere directly. They are expected to take an apprentice or multiple apprentices to further the power structure and to advance towards Lordship.