Hive Mind
The ultimate, supreme grand master awesome badass overlord of all tyranids in existence. The Hive mind blots out all psykic signals such as the Astronomican,astropath communications and even the very warp itself. This is its power. It is nothing less then the collective minds and consciousness of every living tyranid in reality. It is formed from the untold quadrillions of quadrillions of Tyranids and will not die until all said quadrillions of quadrillions die off.
The Hive mind is made of literally every Tyranid creature. The Hive fleets themselves are nothing less then a tendril of the hive mind itself. This means it is big. Very big. Fucking huge, actually. It dwarfs khorne like a speck of dust, reduces tzeentch plans to tears (He needs the warp to manipulate others, and the hive mind blocks that off, bu smothering it with numberless other minds), makes nurgle crap himself in fear and make slaanesh hide under his bed covers. The Emperor himself cannot beat this wall of minds that forms the hivemind. The only two cases were somebody can beat the Hiveminds power is varro tiguirius. (Mat ward wrote that) The other is elder pirate prince eldrad, who was strong enough to recieve a call for help from an embattled craftsworld. (Ahem robbin cruddace)
When a Tyranid goes to battle, it is the hive mind that directs their every action. It can see through the eyes of every tyranid and direct their actions flawlessly. It has the tactical brillance comparable to CREEEEEEEEEEEEEEEEEEEEEEEEEED(As at one point in the Codex it was reported that the Hive mind may have the intellect to turn its defeats in one place to a victory somerwhere else. That means if the hive mind loses somewhere it will win elsewhere. Just pray your at "somewhere" rather then "elsewhere".
If you want to know its full brilliance, then it once outwitted the Ultramarines. There you go.