Given that she just might be my favorite character in all of World of Warcraft, I had to get Chromie immediately.
Chromie is a Bronze Dragon, but she fights in her more familiar Gnomish form. A lot like Tracer, Chromie is a fragile assassin with very high damage potential, especially against enemy players, but essentially no health. Perhaps even less than Tracer, and certainly without the escape moves.
So why play her, other than loyalty to what is obviously the best dragonflight? Range.
Holy crap does she have range.
Chromie has range on par with Sergeant Hammer, and without having to go into Siege Mode in order to get that range. The trick, however, is making sure that you target your opponents well. Chromie will be absolutely devastating if the player knows how to lead his or her shots, targeting where the enemy will be rather than where they are now. Playing against Chromie, you'll want to keep on the move.
Sand Blast is your Q, and fires a ball of sand after a wind-up (this is a theme) in a given direction. It has long range and will only hit heroes. This is both an advantage and a disadvantage, given that you can hit an enemy hero behind a wave of minions but you also won't be clearing said wave. The range on this is very long, so you can hit heroes that are too far away from you to hit back.
Dragon's Breath, your W, will also have a delay, but like Sand Blast, this also has a large range. You can definitely get some cheap shots against enemy structures and minion waves. This will not show a reticle where it's going to land, so if you come at enemies from cover or simply feint, you can often catch your opponents with it.
Time Trap, your E, is far more situational. You put a trap on the ground that lasts for a good long while, and when an enemy walks over it (it's invisible to them,) they'll be put in stasis for a second or so. If you can trap them in one of these, quickly wind up a Dragon's Breath or Sand Blast to take advantage of their inability to move.
Her two heroics are Slowing Sands and Temporal Loop.
Slowing Sands is easily available, but will eat mana for as long as it's up. Still, given the target-leading you'll need to pull of Chromie effectively, you'll definitely enjoy making it difficult for your enemies to evade your attacks.
Temporal Loop likewise will make it harder for your enemies to escape, though it will probably take a little more finesse. You effectively force the enemy to do Tracer's Recall after a couple seconds, making it harder to escape and of course putting them in the line of fire for your shots.
From a distance, Chromie is a total menace. However, she seems to have Murky-level health, so make sure you stay the hell away from your enemies. Dragon's Breath will let you do a bit of wave clear, but you'll primarily focus on enemy heroes when they're about.