Demakes (What game would you wanna send back in time?)

[Gors]

Though I wonder how the fludd would be implemented with just two face buttons in a seamless manner

Use B for fludd and A for jump and that's it
and you can press select maybe to switch nozzles

hold B and you can aim fludd with the d-pad

I'm more wondering what would be the most viable way to handle the liquid "physics" on the NES.

B can only be the run button. Even doki doki panic, which wasn't a Mario game at first, had B dash especially implemented for smb2.