Necron C'tan tricks?

My friend plays Necrons and he told me that C'tan are unique but he said you can field more than one because there are the differenet ones like the NightBringer, The Deceiver, The Void dragon, and The Outsider. Is this correct that he can field the 4 different ones as each is a different model? Or can he only field one because in the codex they are listed as unique? I might be missing something because I don't know a lot about the Necron codex but someone who knows it well, could you explain to me if this is a legal set up to play where he could use mre than 1 of them?

First up, make sure he has the current codex as there are NO named ctan anymore and the current elite choice called the ctan shard is not unique. You are limited to how many and which powers a shard can have though.

As they are elites, so long as he follows the rules for picking the 2 powers per shard, you can field 3 as your 3 elites choices. At this point, shake his hand and congratulate him on giving you kill points and an easy game as your poison weapons destroy his shards