how would I create an ocean terrain by tweeking these

[levlups]

var terrainOptions = { a_zoom: 100, a_height: 7, b_zoom: 50, b_height: 3, c_zoom: 500, c_height: 100 //huge hills 100 regular is 10 };

[EliteAsian123]

I don't know if this would work but, try setting c_height or another one to 0 and c_zoom doesn't really matter, and set to corresponding block to water. There is no way to change the water level if you do this. In the onWorldDataNeeded or whatever it is, you can add simple code after to make water if the block is air.

[levlups]

the water part should be easy , but wath I meant maybe naively , is instead of make a hill going up in the sky as normally it would , how can I make a hill go down below the water level below 0 ,for example, if 4% of land is above 0 in the y axis and the rest 96% is below 0 in the y axis , you have an island biome ,im not sure if we understood each other.

[EliteAsian123]

I believe you can set the height to a negative number to make it dip below 0.