Apeiron King of Light
my idea is to have it close to that of the structure deck.
Use extremely powerful lv 4 water monsters, combined it with the field spells and switch it up every now and then with Umi support and gravity bind.
cards like Abyss solider should be essential in this deck, alone with other lv 4 1800s and its even better if they have effects that can help out.
Levia dragon you can throw in there, but not to many at most 2. You should not rely on it as a regular card, but a finisher with a Umi.
Use legendary ocean instead of Umi more then anything. Have like 1 umi and 2 legendary oceans and 2 of that other one
sweatdrop (the +500/-400).
A couple bouncing cards like penguin solider can help to give you the direct attack that this beatdown needs.
The other one I think is Umirukia or something like that.
Also, like Apeiron King of Light said, try to stay close to the Water Structure deck. It may be a good idea to have 1 "Great Leviathan-Neo Dadealus" in your deck as a backup card.