Tyranid Warrior
A Tyranid Warrior is a type of Tyranid that fills a leadership and heavy-assault role. Warriors are usually deployed at the earlier stages of planetary consumption. As they are synapse creatures,they spread out the synaptic web and guide the lower forms of gaunts in battle. They are also potent foes on the battlefield as they can carry many different biomorphs and weapon-symbiotes and their genus is used as a template to create various elite creatures of the Tyrannic host.
Even the smallest gathering, patrol or raiding party of the Tyranids will most likely be led by a Warrior in order to guide the lesser beasts and keep them connected to the Hive Mind. Think of them as a combination of an elite sergeant and living walkie-takie.
In Game
These guys are fucking expensive but have 3 wounds, toughness 4 and a 4+ save. Unfortunately, this means that they suffer instant death from all weapons strength 8 or up and thus see little play in the competitive field as a single Battle Cannon shot can wipe out an entire unit. In addition, their 4+ saves render them very vulnerable for units priced like TEQs. Mauls hurt them, heavy bolters hurt them, secondary mode hammerheads hurt them, autocannons hurt them, hades autocannons instagib them, manticores devastate them, most barrage weapons ignore their saves. Overall they're quite squishy.
Yes, it is not an easy life for a Warrior as everyone, their grandma, and their grandma's cat all know the most important rule when fighting Tyranids; take out the synapse creatures. And being the most common synapse creatures (not to mention the only ICs in their entire army) and relied on to spread the web they will be targeted first and foremost (unless a rampaging Hive Tyrant or Carnifex is bearing down on them first). Because of this most games will see Warriors bear a great deal of heavy weapons fire and be turned into creamed goo before too long.
In early editions, these things were fucking boss. They could easily match Terminator durability since there was more wargear they could get, and they had much greater flexibility, too, due to how the rules were. You could very easily make a Warrior that was a close-combat death machine, ranged killer, or even a mid-level psychic powerhouse. Or all three in the same unit. In early editions, they could pack on extended carapace or even Warp Field for a good armor save; you could make them winged or leaping; and with the huge number of attacks they had, great stat-line, and tons of upgrades, they were a literal swiss-army commander, one that was extremely popular for newcomers. One might even say they approached pornographic levels of awesome. Sadly the recent edition changes, from about 5th onwards, just turned this mainstay unit into swiss cheese.
8th Edition
Now this is one of the best unit in the Tyranids army, with that HUGE price reduction (24 point with basic equipment, and 20 if you just go with 2 scytals) and the removal of instant death mean it's almost impossible to shoot them down in one hit except with heavy weapons, usually better used on the plethora of 8+ wound monsters tyranids can also field. While the new equipment table is reduced from past editions, they still have everything they need to fulfill pretty much every role on the battlefield, shock trooper, heavy support (now a brood of 9 can have 3 heavy weapon) or simply synapse. With a prime around (also priced down) they even get a boost to hit both in close combat and on ranged, a huge bonus, considering the already good/decent stats of the Warriors, both terrestrial and winged. 3+ to hit and 3 attacks mean pain in close combat, and even with average 4+ to shoot the fact that all weapons they can have have 3 shots per round, makes sure a rain of death comes to the enemy. The winged variants have the same statline and option, but with more mobility and the keyword FLY, that allows them to fallback and shoot, giving them extremely good mobility. Long story short, 8th edition Warriors are absolute monsters, that represent the fluff as well as possible. Extremely powerful and resilient heavy units that will make the enemy shiver in fear.
Shrikes
Shrikes are a winged adaptation of the Warrior bioform, just when you thought regular Warriors aren't bad enough. Fulfilling similar battlefield roles and allowing Synaptic coverage to extend to the fast-moving elements of the swarm, such as Gargoyles and Harpies which might otherwise outrun those Synapse Creatures incapable of flight and be separated from the Hive Mind. While sacrificing some of the protection of their chitin carapace for the ability of flight, few enemies expect an assault of creatures as large as Tyranid Warriors from the skies, thus allowing Shrikes to perform surprise attacks with great speed and efficiency, the element of surprise making up for their relative lack of protection. Their speed and mobility as well as their large selection of biomorphs make them exceptionally flexible, allowing them to fulfill many battlefield roles from surprise assaults directed at the weakest elements of the enemy force, to filling gaps in the synaptic web at a moment's notice.