Notes & Combos
The main gimmick of Umi Horus is that Horus can bait Ash and negate Imperm (Hieratic Sky Dragon), while also giving us a non-Water to make our board un able to be tributed while Kairyu-shin's floodgate is active. Combine this with Gymir's floodgate and your opponent's going to cry. Horus can also increase the consistency of Umi by letting us draw 1 and discarding Ice Barrier.
The only things in the extra-deck that mattered were Dingleberry, Hieratic Sky Dragon, Zombie Vampire, Anemone, Little Knight, and all the synchros. Although Number 90 is in my extra-deck, I haven't crafted it yet, but it can be useful to negate Nib.
The lvl 8 synchros are there for Icejade Ran under A Legendary Ocean, which lowers it's level.
I have two Gymirs because I don't want to banish it with Extrav.
Number 23 can attack directly, then rank into Number 84, then rank into Zeus. It never came up, but I still like having it incase it does. I did use it twice to apply pressure. The opponent removed Number 23 before I could attack.