How do you get special armor for Halo 3?

[Gakis]

I see these people online with like hyabusa knight armor and scout etc. how do I get that? does it increase my hp? or is it just for looks?

 

[Taco]

You seriously have to ask this, you probably won't be able to get them.

They're unlocked via different achievements in the game. Google "Halo 3 unlock armor".

 

[Shut Up Meg]

Get the hidden skulls in campaign mode