While I suspect it will be used somewhat sparingly (if ever), Itachi has the ability to lock people into nearly-unbreakable illusions when utilized against those of his approximate power/skill level and below. However, since this is RP and RP is meant to be Fun, I'm not really interested in a blanket statement of 'it will work on everyone/anyone'! Things shown to disrupt genjutsu are: willpower, applications of pain and the interference of other characters. Things I'm also totally down for messing it up are: any foreign magic 'innate' to a character, any character that's not wholly or recognizably human as he understands it, etc. Characters with strong psychic defenses could likewise be a toss-up that comes down to communication with players! If none of the above can apply, I'm also cool with it just not working Because Jamjar Fuckery.

All instances of use will be opt-in rather than opt-out, and if opportunities arise in a thread to utilize these abilities, rest assured I'll be chatting it out beforehand!

Genjutsu: Genjutsu are the standard 'base' illusions in the Naruto verse. They are techniques which cause one to experience false sensory perceptions to one or more senses depending on the skill of the user. This could involve: body horror, torture or entirely mundane things such as casual misdirection. (ie: your character may walk past something without being able to 'see' it, because in their mind there's nothing there.) Standard genjutsu can be cast without eye contact.

Sharingan/Mangekyou Sharingan: The Sharingan is a specialized dojutsu (or 'eye technique') specific to Itachi's clan. The base Sharingan improves one's own innate genjutsu talents, and the Mangekyou Sharingan does that in addition to having access to new illusory abilities (generally) unique to the caster. (So, even if two people both have the Mangekyou Sharingan, they will not necessarily have the same illusion techniques at their disposal) The weakness of genjutsu cast by both the base Sharingan and the Mangekyou Sharingan is that it requires eye contact.

Itachi's specialized Mangekyou Sharingan ability is called 'Tsukuyomi', a dream world that he controls all aspects of down to one's perception of time, pain, etc. Using this ability comes at great physical cost to him and tends to weaken him considerably, he will likely not be using it unless there's a significant need.

If you're cool with having genjutsu cast on your character, let me know! This isn't a guarantee it will happen, more of a 'these are the people that might be okay exploring it should a plot arise or situation call for it' sort of deal.