Power of the final boss (full lore spoiler)

[Slim_Cognito]

This C'tan might just be the strongest Void Dragon Shard shown so far, yes stronger than the Void Dragon Shard that fought with the Emperor and the other Void Dragon Shard that destroyed 12 Necron Dynasty worlds when they were trying to capture it. And possibly the 2nd strongest C'tan Shard currently in the lore only behind the Deceiver Shard in Infinite and the Divine. Unless the Silent King's Burning One Shard is also OP since the leader of the Necron should have a OP Shard.

But to list a few of it's powers from this game according to the ending slides

Powerful enough to create dimensional barriers to cover a sector sized region of space which is massive!

"Created dimensional barriers that cut the Koronus Expanse off from the Imperium more soundly than the Great Rift"

If you go the Chaos route than the Chaos gods orders you to enslave it with the Yoke which is a modified Tesseract Vault.

"The strange entity, imbued with a silver of a Star God's power, was beyond the reach of the rulers of the warp. And as such, they were dangerous and destined to be enslaved."

But that doesn't last long as the ending slide image later shows the Void Dragon Shard destroying the Yoke Necron machine from within and then proceeds to fly through space to destroy every Necron tomb world in the Expanse.

"Leaving the Necron systems behind, the Star God vengefully obliterated every Tomb World of the ancient xenos race. The old hatred of the C'tan, betrayed by their deathless servants, whispered inside him."

For those asking how did we beat it, it was because the Yoke(modded Tesseract Vault) already weaken it's power by a huge amount at the very start of the fight. And also the Shard wasn't even paying any attention to us until after the fight when it's struggling with the Yoke.

"the Yoke has started the binding process! Most of the entity's power will be restrained by the machine. Whatever is left is still potent enough to kill us all. Weaken its physical shell and distract it, and I will control the Yoke and try to chain the monster"

"Only now does the C'tan Shard turn it's focus on you, for the battle was nothing more than the reflexive resistance of an alien mind absorbed in a completely different range of thoughts and responses."

You can also gain the favor of the Chaos gods but choose to serve this Void Dragon Shard at the end. This will piss off the Dark gods because you gain their gifts and then betray them for a mere Shard. All revenge attempts the chaos gods do by sending daemons and their mortal champions to get revenge on you would fail because of the Void Dragon protecting you.

"The Dark gods were enraged by their champion's betrayal, so quick to accept their generous gifts, and yet so eager to trescherously abandon them for a new master. However, neither the wrath of the masters of the immaterium nor the weapons of their loyal warriors could harm the one protected by the power of a true deity."

We are starting to see some extremely powerful C'tan Shards out there like this one and especially the Deceiver Shard from Infinite and the Divine. Wonder if we'll see even more powerful Shards in the future.

And to think this transcendent Void Dragon Shard is still a very small portion of it's full self. Guess it's no surprise how it was able to take on a Eldar God with 7 Blackstone Fortresses back during the War in Heaven.