Hi, talin
I was playing around with the icon and I realized that getting depth in a 16 by 16 space is incredibly hard. So I think maybe going in a different direction may be the solution. Icon’s should be well “iconic” just a little thing that’s easily recognizable and symbolizes something larger.
So I dug a little bit through google images for hydra related things and found these old pots. There are a lot like them and have bright colors and great silhouettes. Kind of reminds me of the old Disney movie with the pictures of his deeds on pots.

So with that said, here’s an rough edit

I realize this is probably not the direction you were thinking of, but hopefully I was helpful.