An OTK deck but can hold it's own while stalling and against dragged out fights. This deck is great because aside from it's OTK potential it has another setup that could win you the duel. The key card Sea Stealth Attack is very versatile acting as both protection and destruction. The skill Menace from the Deep puts pressure on your opponent because of the 2000+ attack monster hitting them directly in the face, and sometimes allows you to perform your OTK.
[Menace from the Deep] Can be used if "Umi" is on the field, and you have a Water-attribute normal monster on your field. That monster can attack your opponent directly. this turn. At the end of the Battle Phase, that monster is sent to the Graveyard. This skill can only be used once per turn.
Always have A Legendary Ocean on the field. You should never be without it anytime in the Duel. It opens up opportunities for you to summon your beaters, use your skill, and gives the powerful Sea Stealth attack it's effect. You can send Warrior of Atlantis from your hand to the grave and search A Legendary Ocean from your deck. When A Legendary Ocean is in the graveyard you can activate Sea Stealth attack to retrieve it.
Sea Stealth Attack is a very powerful and versatile support card for any deck with A Legendary Ocean at it's core. In fact it is the next key part of your strategy, only next to A Legendary Ocean so you want to have it active on the field as early as possible. If you have at least 1 WATER monster on your field, you now have access to unlimited protection for your face-up backrow, which is very important in a deck which relies heavily on it's field spell. You also get the equivalent of no cost once per turn monster removal if you have Giga Gagagigo or Terrorking Salmon on your field. A good combo for this is attacking directly with your Normal WATER monsters using your skill and then remove them from play with Sea Stealth attack so that they can come back and stay on your field during the end phase.
These two monsters were specifically chosen to synerize with this deck's strategy. Both of them are Level 5 WATER monsters, meaning you can Normal summon them as Level 4 monsters if A Legendary Ocean is on the field. Both of them are also Normal WATER monsters meaning with the skill Menace from the Deep you can attack your opponent directly for 2600+ damage. Sea Stealth attack can turn them into protection effects for your face-up backrow by removing them till the end phase, and also turn them into monster removal by destroying any monster they attack before damage calculation.
Once you get A Legendary Ocean and Terrorking Salmon/Giga Gagagigo on the field, you can use the Back-up Rider and Hey, Trunade in your hand to go for an OTK. Use Hey, Trunade to clear your opponent's backrow of any set cards which could disrupt your attack. Then use Back-up Rider on your Terrorking Salmon or Giga Gagagigo to bring it just above 4000 attack. So that you can instantly finish your opponent without disruption when you attack directly using Menace from the Deep.
Staunch Defender is really handy. If you half shut Slim, you practically win, even against Toons. Alternatively you can use it to force your opponent to attack a turtle, and give yourself another opportunity to attack.
Econ isn't super handy in this deck. Forgotten Temple more or less acts like a persistent Econ. If anything, Chaos Zone might be better.
Why isn't econ handy? Turtle semi floats so you can do econ take play with it. Eg. direct attack with lancer, banish with temple, ss turtle, steal opponent mons, direct attack again for game. Handy against opponents with BIG mons like red eyes etc. Also can be used for defensive play. Chaos zone seems too slow for this deck to be useful. Is slime not dead too often? Without supervise, its useless
I didn't find Econ too handy because most of the time it just sat in my back row. A lot of the utility of screwing with your opponent was covered by FTOD, but maybe I should reexamine it.
Chaos Zone isn't as slow as you'd think. You get a banish in your turn and your opponent's turn, that's half a summon right there. Problem is that it's only worth it if you get it early, and only then.
As for Slime, I've found it to be an MVP. Arm Shield, Half Shut, and Supervise can all give it the turn it needs to summon. Not to mention if it gets resummoned by Supervise, it's ready to deal damage again next turn. And worse comes to worse, it can keep the turtle engine running.
If anything, this deck needs a third half shut, but it's too expensive.
I feel like this deck has potential now, especially against relinquished but no one farms mako. It also seems very underpowered aganist harpies which is a problem