La Mulana's fourth children, the Fish Men, were cast out by the mother just like all the other children that she created…but near as I can tell, there's no reason given as to why they were forsaken.
Do any of the tablets hint at why they were cast out like the other children? Or is it left completely unsaid?
Best Answer
There are two answers.
They Weren't Cast Out
In the room with the Big Brother's Shop, there is a tablet that says
This is also part of a puzzle solution in the Gate of Guidance in the remake, though the fourth child isnt mentioned there. Seeing as nothing mentions the Mother destroying them, she never did.
They Ran Out of Time
The Mother is not very patient with her children. Rather than letting the Snake-Men go about their business, she cast them out for not knowing her wishes. The Mother is going to cast us out as well, about thirty-four years after the time frame of the game, according to a tablet in The Temple of Moonlight.
So, the Mermen were unable to return the Mother to the Heavens before she decided that they weren't going to do it.