Like NoFreakingWay, I also made up some nen abilities on nexgear before it went down. I also ran the RPG there (thinking of restarting one here

).
If I lived in the HxH universe and it turned out I was of the Emission type, this is the ability I'd like to make:
Name: Fūjin Shuriken
Type: Emission (primarily). Would also incorporate Manipulation and Transmutation
Summary: I form (Transmutation) the shape of a
fūma shuriken out of nen and throw it (Emission). That would be the basic form; a simple, aero-dynamic projectile attack.
In order to activate homing (the main use for the technique), I would have to meet the following
conditions: dodge at least ten attacks from the intended target of the homing whilst being no more than 1m away from said attacks, then call the word 'Trace'. This would confirm the homing target.
Once a target has been confirmed, any Fūjin Shuriken I throw will direct themselves automatically towards them (Manipulation). After one week, the 'trace' disappears and I have to meet the conditions again to reselect them as a target.
The distance the shuriken would travel, how fast it would move, how long it would stay airborne, the quality of its homing ability, its destructive power, and the time it takes to form would all depend on my mastery of the technique (ie. as I gain practice and experience using it, it would fly further, faster, longer, home better, be more powerful and it would take me less time to charge it up).
Restrictions: Only one target can be 'traced' at a time.
To release a target (in order to select a new one) I must form the Fūjin Shuriken and say 'release' (or wait until the week is up).
I can have no more than two Fūjin Shurikens formed at any one time.
Commentary: I picked a shuriken because I didn't want to just have boring old nen bullets, but at the same time I didn't want a complicated ability. That, and they're cool (hey, gut feeling is important!). The fact that I change the nen's shape involves incorporating Transmutation, but what the hey. The shape it is will increase its aero-dynamics, allowing it to travel for longer and turn more easily to chase a target more effectively.
As to the conditions for homing, I chose dodging because my reflexes are pretty good. I chose dodging rather than blocking because I don't want to run the risk of having to block a massive attack from a powerhouse whose attacks I could dodge instead.
I chose 1m because it's the closest I can get to an opponent realistically without being on top of them. Also it means I can't stand a mile away from someone while they happen to attack something/someone, and then claim I 'dodged' their attacks, simply by virtue of their not having hit me.
The basic tactic would be to get in close to my enemy, engaging them in close combat, dodge some of their attacks and 'trace' them, then gain some distance from them (easier to do if I have back-up or a partner who I can tag in), and then charge up the shuriken and lob it. I put a restriction on the number thrown to a) increase their individual effectiveness and b) prevent me throwing a hail of them at my opponent, but still leave me with the option of throwing a second, so my target has twice the difficulty dodging.
Phew, took my longer to describe what I think is a pretty simple ability than I expected!