system
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human
[Warhammer 40000] From greatest to least what is the strongest Tyranid Units?

Like a Carnifex can probably kill a genestealer and so on.
gpt
The Leviathan Bioships are probably the biggest single Tyranid organism there are. They are at least the size of a battle cruiser, has lots of tentacles and being concentrated neural tissue they are the main nodes of the hive fleets' hive mind. They also have space ship scaled psyker-like abilities and also project a shadow in the warp that can block astropathic transmissions.

Most hive ships would crush any of the land based organisms, so we'll go to the land based ones.

Bio-titans like the Heirophant are probably the biggest land-based organisms that aren't spires. They are covered in gun-form organisms and heavy chitin plating. They also have void-shield equivalents. They can squish most organisms pretty easily.

Trygons and Mawlocs are big (they're pretty much on the scale of super-heavies) and surprising since they are burrowers. They can take on carnifexes easily usually by ambush. 

Carnifexes can probably take on any of the equivalent sized organisms except hive tyrants. Hive tyrants generally have better weapon organisms and are considerably smarter. So both carnifexes and hive tyrants would easily take out medium-large organisms like Biovores (artillery), pyrovores (fire support), Lictors (scouting and infiltration) and warriors. Brood lords are pretty big and intelligent so they'll give carnifexes a good fight. 

Zoanthropes are a bit weird. They are physically weak but extremely strong psychics, they could probably demolish most of the above up to carnifexes easily but will fold if anything looks at it funny, or gets close. 

Biovores would blow up any of the fodder organisms. Same with Pyrovores and their flame/chemical spewing. Lictors will mostly win, but might be close against a genestealer. Warriors should win one on one against any of the fodder. 

The fodder mainly have numbers on their side. Genestealers will probably be at the top with their speed and rending claws, although ranged Hormagaunts and Gargoyles might give them trouble if they fire first. Termagaunts are probably the bottom of the fodder. 

Below the fodder would be the Scavengers like rippers and then below that would be the micro organisms that infect the flora and fauna to supercharge their growth. 


A lot of organisms will obviously do better if they're in their niche or the conditions are right for them and most of the weaker ones (fodder) are designed to be deployed in large numbers to overwhelm enemies.