With the 25th Anniversary Rarity Collection, I decided to edit this deck for real tournament play, since these cards are all affordable now! Yaaaay! The most expensive card in here should be Zeus, with Watthydra second having only one printing. I built it for going first. Obviously those sd ed monsters aren't meant to be taken to tournaments, but they give you ideas for more options. The handtraps in the sd are more of what this deck needs: Removal and denial. And there's Hamon Lord of Striking Thunder because he's a thing you can do here. Not an ideal thing, but a thing nonetheless. I added 1 Wattsquirrel in the main deck so we don't have to rely on Kyuki alone to make Hydra.
It would be extremely satisfying to see Watts become a new rogue deck, especially now that they finally have a combo! Wattuna is effectively a 2-card combo. You attack with your other level 4 Watt first, then summon it from hand to attack again, then special summon Wattkyuki using Tuna and your other Watt on the field, then after Wattkyuki attacks, shuffle Tuna from gy and Kyuki into the deck to special summon any other Watt synchro regardless of level except Kyuki. If this goes uninterrupted, you're looking at 4800-5100 damage minimum, depending on what other monsters you summon. And that's before buffs, which cards like Hip Hoshiningen and Galaxy Photon Dragon give to light monsters, like all Watts.
Wattkingdom cancels opponents' summon effects in the same column, and that stacks with each copy and Watt monster on the field. Fill up those extra columns first so you deny links. It also finally gives us a way to summon more than one Watt on the first turn without having to wait for that Wattrain in your gy, meaning we can now do extra deck plays. You'll probably want to do that after the battle phase, though. Like summoning Bagooska after smackin' your opponent. Imagine opening a hand with 3 Wattkingdoms and a Watt monster. Your opponent gets to do nothing on summon without that limited Harpie's Feather Duster or semi-limited Lightning Storm (or any Simorgh deck). I added Pot of Prosperity to dig for any combo pieces you need for Kingdom. Yes it halves the damage opponent takes, but it does not negate it, like the next cards that are no-nos for Watts.
3 popular cards you should absolutely never use with Watts are Evilswarm Exciton Knight, Dark Ruler No More, and Evenly Matched. This deck needs to deal damage in the battle phase, which all 3 of those prevent. I know your opponent can put up big, daunting boards with their meta wombo-combo deck and you wanna get rid of them, but firstly, without Exciton, these monsters can't remove anything permanently, and secondly, you sacrifice your one win condition to clear their field once and then get blasted next turn. So be smart, and don't do that.