You can find this Power Moon in Quadrant D2, atop the Beach House, but the seed required to grow the Power Moon is in an inlet to the East.
Warp to the Beach House flag then head East until you hit the inlet with seaweed enemies inside it. Look for the gold seed on a rock at the bottom of the inlet. Grab it and head back to the Beach House roof.
The Seaside Kingdom Power Moon 23 – Sea Gardening: Inlet Seed is one of the Power Moons in the Seaside Kingdom.
Throw the seed in one of the planters. It will take some time for the seed to grow naturally, but you can use the Gushen's jetstream to water the plant and make it grow faster. I recommend planting all four seeds, then watering them all at once for maximum efficiency. Once the plant is grown hit the golden bulb with your hat to reveal the Power Moon.
If you look closely at Mario’s eyes, you’ll see that the iris is off-center. There’s a thin crescent of white on one side and a thicker crescent on the other. The thin crescent goes down. Just getting the eyes right will make your score a lot higher, as you can see in the second and third images above. In fact, getting the eyes on the right sides gives you a lot of wiggle room.
Just like every other kingdom, you can grab this moon from the Crazy Cap shop for 100 coins.
To the west of Peach’s Castle, there’s a large well with an 8-bit pipe sticking out of the side. Head in and run all the way around the well counterclockwise to find the note. Sprint back around clockwise, then exit the 2-D world. There will be another ring of notes outside. Just run into the middle of the ring and spin toss Cappy.
21. Mushroom Kingdom Regular Cup and 22. Mushroom Kingdom Master Cup
There are two kinds of collectibles in nearly every Super Mario Odyssey kingdom: power moons and coins. In this guide, we’ll show you where to find the Mushroom Kingdom’s power moons.
The trick to winning both the regular and master cups in the Mushroom Kingdom is using Rocket Flowers. As you can see in the image above, they’re peppered throughout the course. Just keep grabbing them with Cappy and rocketing toward Peach’s Castle, and you’ll beat the competition.
On a ledge above the Goomba Woods, a little to the northeast of Peach’s Castle, there’s a brave Toad guarding a moon in a small alcove. His weakness, though, is Goombas. Drop down into the Woods and capture one or two. Do a wide loop to the east around the pool to return to the Toad. He’ll get out of the way, and you can claim your moon.
18. Forever Onward, Captain Toad!
Captain Toad is in this kingdom, too. This time, he’s right on top of the Crazy Cap shop. Use the crates nearby to backflip up and dive onto the roof. Talk to Captain Toad for your moon.
For these two, you’ll need the Mario 64 Cap and Suit from the Crazy Cap shop — they’ll cost you 35 purple coins. Head to the cliffs between the north side of Peach’s Castle and the Goomba Woods. There’s a Toad watching a locked door — he’ll only let you in if you’re wearing the Mario 64 outfit.