I agree that if it came to a conflict between the two races, the necrons would win purely by dint of outlasting their opponents. Tyranids may be insanely strong but they have biological needs that the necrons just don't.

Easy, the tyranids will start seeding orks for food.

Ironically enough it was a battle between necrons and tyranids that got me into 40k, it was back when I was in secondary school (high school) I'd never heard of 40k or seen it before, but one day some of the older kids came in to the "social club" which was just a place for nerdy kids who didn't wanna play out side to hang out. One had tyranids and the other Necrons, I was instantly drawn to the Necrons, I sat there and watched them play, asking questions and no dout irritating the player some what, being a dum kid at the time, pestering the older kids. But they let me watch and once they had finished the Necron player even gave me a Necron warrior! As a starter for my own army, for my 14th birthday that year I got my first Necron army, been hooked ever since.

This is everything I needed to stroke my massive Necron Ego

There is no ultimate answer to who would win. Yes Necrons counter Tyranids pretty hard, but a) nobody knows what kind of crazy tyranid types are out there (we only know that we know little about the Tyranids) and b) the actual amount of Tyranids is unknown as well (there COULD be a million times more Tyranids waiting to invade the galaxy). The main question is simply: is it worth it to fight such a wasteful war against the Necrons? The Hivemind could just decide to invade another galaxy with less local resistance.

Pfft, sly Marbo beats all

question: can a dreadnought do a backflip???

Sci-fi writers have a horrible sense of scale, so the numbers quoted for the Tyrannides are so ridiculously large that they outnumber the necrons at least a million to one. Not that it seems to matter much since a couple dozen Space Marine chapters numbering around a thousand soldiers each seem to win something like a tenth of all battles fought in the galaxy.

basicly it's lawful vs chaotic evil

Tyranids would easily adapt to necrons. Necrons may not be organic, but that just means tyranids would need to learn to absorb inorganic material. Basically becoming more like xenomorphs.

"When the end times come, it will be the Necrons, and the Tyranids"

The real question is.

Necrons are badass.

Lets just say their is a reason why the Tyranid hive fleets avoid world's

4:39

Necrons be like: "I ain't got a soul but I'm still a soldier"

One thing to remember about Gauss, It does not actually fire toward an enemy, it pulls from the enemy. Its essentially a power ionic/magnetic weapon, it pulls molecules apart through sheer magnetic force. The hint to its nature is in the name. How they accomplish this is another matter entirely.

I remember in either an older necron or tyranid codex it mentioned that a hive fleet completely avoided a necron tomb world due to the psychic dampening field that it produced. I don't know if they have retconned that or not but the necron would completely disrupt the hive minds control over the swarm if they have not.

When he said "zombie con the movie", I heard "zombie condom movie"🤣

Necrons have to be the worst matchup for tyranids; Necrons have no biomass for them to consume, and necron gauss flayers destroy organic matter entirely, meaning the hive fleet wont even be able to harvest their own dead troops. Add to that that Necrons may have motives to attack tyranids due to them attacking and destroying the lesser races they could use to recover orgaic bodies, but tyranids would have little interest in attacking necrons as their world are often void of life down to the bacteriological level. Tyranids are not a direct threat to the Necrons, but they can threaten the necron's objectives by consuming all organic races.