Object/Psea
This is the sea on GCN Peach Beach.
It floods and drops with a certain time, changing his height (Y coordinate).
If you want Psea on your track you have to do some things: first, on your model create two planes, one at Y=0 (fifth and last "layer" of the sea, the lower; deep water, fall boundary) and a second at Y=240 (first "layer" of the sea, the highest).
For a strange and unknown reason the position Y=0 of Psea in game is at Y=9860 on a 3D editor, so raise up your planes of these units.
Psea raises itself of 288 units to arrive at max height, so the "fall boundary" level of your track is at Y≤10148; "dry locations" are at Y>10148+240, that is Y>10388.
Naturally you can create your track at different heights, moving Psea of the corrispondent height in the KMP file; X and Z transformations don't give problems if values aren't very big.
If you want to create a Psea specifically for your track, you have to create 4 new polygons in your model, each one at different height for each "part" of original Psea:
1 → Psea1sand, Y=9648
2 → Psea3nami, Y=9600
3 → Psea4tex and Psea5spc, Y=9590,4 (are coincident)
4 → Psea2dark, Y=9336
Recommended shapes are hexagones and square; they can be identical or you can make them one bigger than other: in original Psea 1 is the smallest, 4 the bigger and the other two proportionally big.
Now export as OBJ each polygon and import in SZS Modifier in every corrispondent subfile; in KMP file coordinates of the new Psea are (0; height (see above); 0).