Night Scythes, also known as Flying Space Croissants, are a flying piece of Necron technology introduced in 5th Edition that, at the start of 6th edition is one of the many reasons people called the 'crons Mega-Cheese. Fluff wise though, these are your transports to your Doom Scythe fighters.
Unlike most troop transports however, these craft do not contain any transportation compartment. Instead, they ride into battle with a captive wormhole linked to a distant Tomb World built into its hull. As all Necrons are made of inorganic Necrodermis, they don't really need to care about any adverse affects of that wormhole. This concept has actually been in 40k for a while, as back in Epic, Eldar had the Storm Serpent super-heavy transport, which functioned basically identically, only with a Webway portal.
Despite their emphasis on transportation, these vehicles are armed with twin-linked Tesla Destructors and are still formidable craft in their own right when compared to the attack craft of lesser races.
On the Tabletop
Starting with 5th Edition, the Night Scythe provided the Necrons with a flying transport option. While a flying transport's not all that weird (after all, the IG have Valkyries and the Space Marines have Thunderhawks), the Night Scythe had some things going for it that other flying transports didn't, which is why it was regarded as a cheese machine before everyone got decent anti-air:
- Firstly was that it could be taken as a dedicated transport, this at the start of sixth edition meant that you could flood the board with these, if you couple that with their extremely fast speed and pretty decent weaponry your opponent would have no reasonable way of dealing with them. Sure they were a bit pricey but their durability (remember that back then nearly everyone needed 6's to hit them) made them almost guaranteed to make their points back.
- The second (and very minor) difference was that if those other flying transports crash, they can potentially kill members of the squad it was carrying. If a Night Scythe crashes, since it technically uses a wormhole to another area to move troops around (similar to the monolith but smaller), the Necrons waiting "in" it enter ongoing reserves instead (though they cannot deep strike), denying your opponent a much weaker unit to score an easy kill point off of.
In 7th Edition, they were still awesome. A little pricier... but still just as awesome as ever. Moved into fast attack... so... Fast attack your opponent off the table! Stay focused on your warriors of course, but you wont regret it.
9th Edition Zoomer Primer
It may not look like it at a glance, but this is the most dependable transport in the Codex. Its statline is fairly unimpressive, being T6 12W with 20-50" movement (it comes with all the usual aircraft quirks) with unfortunately still no protection rules. Though at least it is much cheaper than the horribly overcosted Doom Scythe. As well, it is equipped with a pair of fairly awkward Tesla Destructors (10 shots at S7 AP-0 D1 + tesla rule). On the plus side, that is a decent amount of shots and statistics dictates you should be able to get one or two exploding 6's ; on the other hand, no AP on a weapon with little synergy doesn't feel good.
But that doesn't really matter, the damage it will do directly is mostly just a nice bonus for its utilitarian purpose: ferrying infantry all over the map. With a transport capacity of 20 (double that of a Ghost Ark) and the perks of being a flyer, it can easily dash behind the lines and drop a massive blob of Warriors where your opponent will least want 40 shots of Gauss fire. Granted, you'll need to pay the CP for Prismatic Dimensional Breach, and your dudes won't have MWbD, but it's worth it.