This is the ability to create identical duplicates of himself, with strange and startling affects. Unlike most powers better classified as Replication, Julien cannot create totally instantaneous clones, or reabsorb them — rather than generating illusion-based duplicates or duplicates made up of some less than real quality that allows them to appear and vanish at will, Julien must physically grow bodies out of himself, and he can really only do one every few weeks unless he pushes himself or is amplified. There are two methods.
One of them is a kind of instantaneous duplication, wherein he can grow another clone out from himself within a matter of seconds. This can only be done during a moment of extreme panic, fear, anger, or otherwise heightened state wherein adrenaline is pumping. This also has a massive energy cost for himself — his other powers will be dampened for the next 24 hours, he will feel physically unwell and weak if he doesn't simply pass out. The clone is better off, physically, but will not have taken on any abilities when it is produced, and within an hour, it will start to 'degrade' — become mentally blank, and very physically weak with a strong chance of dying. However, during the hour it survives, it is healthy and capable of obeying psychic commands from Julien, the strongest of which can happen during its formation, and the power of these commands will decline over the hour.
This stunt can be better achieved if Julien is augmented at the time — he will experience lesser costs to himself, and the clone will not degrade, or at least, will survive to be its own person once it recovers from the "severance" process. However, it will still be instinctively obedient to Julien if it survives, but still retain no other powers.
The second method is more intensive and arguably more effective, depending on what is required. Over a period of two days (or quicker if augmented), Julien can "vegetatively" grow a clone from an embryonic state into a full person, with a kind of umbilical cord system. It is a vulnerable state to be in, as he will be low on personal energy or even consciousness, maintaining a trance-like state throughout the process. If the cord is cut before this is complete, the clone will instantly die. If the process is allowed to be complete, both clone and Julien will be healthy (if thirsty and hungry, for the latter) and functional. This slower method has several benefits — powers are able to be copied/transferred to the clone, and the clone will suffer no degradation. The clone will also be their own person by the time this is complete, unless Julien administers himself certain sedatives through the growing process, which seems to make the clones more amenable to suggestion and brainwashing, which will be a lasting imprint as to who they will ultimately be. He can also create more than one clone at a time via this method — any more than four may have permanently damaging affects on him, however.
Scars and tattoos do not carry over. If the "root" dies, the clones will die. They cannot be reabsorbed.
The final thing to note would be Julien's interaction with his clones — they do not do what he wants them to do, necessarily, unless some of the above techniques are employed (augmentation during the quick process, drugs and medical oversight during the second) and even then, it is not the same as having duplicates at his beck and call. They are, ultimately, separate people. He does maintain a measure of psychic contact with them, and the more independent they are, the harder it is to maintain.