This is quick low quality render. What should I add in background/foreground? Lighting?
I would suggest adding some variation to the shrooms, like a different material on the top and bottom. Also these are quite large plants and perhaps old so some signs of aging and weather like mold growing near the bottom and discoloration at the top. Less gloss overall for everything in my opinion. Also I like the water on the first render more than the second one for some reason.
Maybe add something like stars or a cave background behind them.