This is a quick deck I came up with, intended to try and use Sea Serpents, the least supported type in the game. I'm intentionally using only Sea Serpents, although I may add a few others if they help. I'm looking for any suggestions of other cards.
1x Ocean Dragon Lord - Neo Daedlaus
2x Levia-Dragon Daedlaus
2x Armed Sea Hunter
2x The Dragon Dwelling in the Deep
3x Deep Sea Diva
3x Mermaid Archer
3x Spined Gillman
1x Heavy Storm
1x Mystical Space Typhoon
1x Brain Control
1x Level Limit Area B
2x Moray of Greed
3x A Legendary Ocean
1x Torrential Trubute
1x Call of the Haunted
1x Gravity Bind
2x Forgotten Temple of the Deep
2x Aegis of the Ocean Dragon Lord
2x Tornado Wall
2x Sea Dragon Lord Gishilnodon
1x Brionac Dragon of the Ice Barrier
The goal of the deck is to use Gravity Bind/Level Limit to lock your opponent's monsters, and then use Mermaid Archer and Armed Sea Hunter to attack. Codarus can clear any awkward spells or face-downs, and Spined Gillman and The Dragon Dwelling in the Deep provide more power-ups for attacking monsters. Levia-Dragon Daedlaus and Ocean Dragon Lord can wipe the field for you to attack directly. Salvage allows you to reuse many, and Moray of Greed lets you swap them for new cards from your deck.
I know this isn't a top class deck, and I may well not even build it, I'm just looking for any suggestions on improving it.