TIE Scimitar
When Grand Admiral Thrawn returned from his missions on the galactic fringes to wage a campaign against the New Republic, the TIE Scimitar was developed and commissioned on his orders. This heavy bomber design also seems to have reached the forces of the Palpatine Clones on Byss. [The fugitive Royal Guardsman Kir Kanos possessed a TIE Scimitar in Crimson Empire.]
The hull is an elongated unipod design, with the cockpit extending forward beyond the wings to provide superior crew visibility. The two crewmen enjoy extensive viewport strips along the cockpit ceiling, and below to port and starboard. In an emergency, the entire cockpit pod can detach to jettison the wings, main hull and payload.
A TIE Scimitar is propelled by a single ion engine, augmented by a pair of powerful manoeuvring repulsor drives mounted on the wings. Repulsors are the most efficient form of propulsion within the gravity well of a significant planetary body; and bombers naturally spend many missions attacking ground targets.
The wings are an unusual shape: scalloped so that the panels turn back slightly around the pylon. This increases the craft's forward or rear profile, and hence its vulnerability to enemy fire. The explanation for this design compromise is not obvious. It may be less a concern for this bomber than other TIE designs, since the Scimitar is equipped with strong shield generators. It may be an aerodynamic concession of some kind, owing to the fact that these bombers often operate in atmosphere; or it may have something to do with leverage and the action of the repulsors to turn the craft.
TIE Drone
This is a droid/computer controlled starfighter mass-produced from the factories of the World Devastators of the Battle of Calamari and the Shadow Hand campaign. The vehicle is often called a "TIE Droid", although it would be more specific and appropriate to call it a TIE drone instead, since a "drone" is literally a starfighter with artificial intelligence whereas "droid" usually refers to an independent ambulatory android that could be separated from a vehicle. SFS had experimented with drone TIEs for many years, but they were impractical as long as the Empire dominated the sapient and material resources of the galaxy. The drone fighter's programmed piloting and combat tactics tend to be idiosyncratic or inferior to a living pilot. Therefore the ability to mass-produce it is the only major advantage. The TIE drones are deployed only in overwhelming numbers, and in situations when the efficiency of manufacturing outperforms the effectiveness of Imperial pilot recruitment and training.
TIE Phantom/TIE [V38] (Sentinel?)
A fighter design which apparently was well-known in the STAR WARS universe but thusfar has only been glimpsed in the literature in the form of a modified cloaked variant. At this time we have no way of knowing which of the Phantom's features are shared by the parent model. The basic hull, engine and wing configurations are probably the same; if there were fundamental changes then Ackbar would not be justified in calling the cloaked ship a mere modification. The cockpit is certainly a standard TIE ball, attached to the main hull, rather than the makeshift conical alternative used on the transitional Phantom.
The military and colloquial names for this fighter have not yet been revealed. The technical designation used by Admiral Ackbar is V38. Perhaps it would be listed as TIE/V on tactical displays (with this ship being the 38th sub-model), and the common name (analogous to "Interceptor" or "Defender") beginning with a "V". Alternatively, it may be the "TIE Sentinel" mentioned in the Hasbro online survey; this designation fits the V38 better than its cloakable descendent. Of course these speculations may actually be meaningless, since the Galactic Empire does not use the Latin alphabet and all fighter designations are translations from Imperial Basic.
The three wingtip cannons on the TIE Phantom may be a hint at the role of the mainstream TIE Sentinel production model. If these weapons are ion cannons they would compliment the laser cannons on the cockpit chin, and also would help to round out regular TIE starfighter forces, which generally lack ion cannons. The absence of ion cannons on common TIEs may have a tactical reason, or else it due to technical constraints (eg. ion cannons may require power systems that are not easily contained on compact starfighters). The TIE Sentinel is not a rare vessel, but not a dominant and common design either. Its tactical role must be special in some way, and the ion cannon hypothesis seems a good possiblity (though not a unique solution).
(TIE Phantom)
This is a little-known experimental two-man fighter produced in limited quantities at a secret facility sometime before the Battle of Endor. According to Admiral Ackbar, it is a modified version of an extant fighter model called V38, with the most important addition being a special set of sensor/scanner countermeasures.
In the computer game the prototype craft appeared to be named "Phantom", but the term "TIE Sentinel" has also appeared (most prominently in a Hasbro online survey about future toy concepts). Most likely a TIE Sentinel is the V38, lacking a cloaking device, and the cloakable experimental fighter is the TIE Phantom.
The triple wings total a radiator area equivalent to over double that of a TIE interceptor. There are three engine outlets in an equilateral triangular configuration on the stern, which is a flat rather than spherical surface.
The cockpit configuration is unusual; it looks more like part of a Corellian freighter than a spherical Sienar design. This may have been used only on prototypes; production models, had they ever been built, probably would followed SFS conventions. Crew enter through an elevator hatch under the primary hull.
The vessel is armed with two chin-mounted laser cannons in addition to the three which appear to be mounted on the wingtips. It also carries some remarkable power-consuming extras, which might reduce its propulsive performance to something less than an older fighter or bomber. These luxury devices including a shield generator, a hyperdrive, and some sort of cloaking device which is capable of operating even during a hyperjump.
The latter feature is most surprising for a ship of this size. The Imperial Navy only used cloaking devices for very special tactical purposes, and full cloaking shields were technically impractical on anything but large warships or cargo vessels. A cloaking device mounted on a starfighter must have some drastic hidden or overt drawbacks. Perhaps there are dangerous side-effects for the pilot? Perhaps the fighter contains a compact but unstable energy source that produces a gargantuan explosion when the ship is crippled? In any case, the cloaking devices on the prototypes were flawed, the cloak effect tended to flicker on and off, and was prone to outright failure.