Allright, here is my entry to the art contest. It may look a bit weird, but bare with me - I had a reason for such design choices.
And here is the mask reference sheet:
Ok, now for the explanation: The challenge of envisioning the design of Helryx comes with the idea that she is the very first Toa , very primitive and somewhat fragile. So with this in mind I came to conclusion that her armor should resemble shells of very early creatures, like crustaceans from the Cambrian period - time when Earth was completely covered with ocean, and first complex life forms started emerging (and most of them were like crayfish, shrimp and other little guys with shells). And that most important is - this Cambrian theme fits very well with Helryx being ancient, and being a Toa of water, In my humble opinion, of course. С:
I hope you enjoyed my artwork and this little paragraph and Good luck to the other contestants!