Ok, so I put the mustifar asset (I think it was like Mus_world1 or something. It has flowing lava (I think it is animation.) Anyways, when I put it in Zero edit it shows up but when I load my map it crashes. Is there something I need to change?

can you post your errorlog please?

did you copy over the "munged" folder from assets/worlds/mus also do you have all the right textures ( i doubt it is either of these issues and I have to agree with D.U.C.K. and say post your error log).

I thought Mustafar lava was just a lava prop with a scrolling texture. And a one-second safari into the Mustafar animations folder reveals no lava anims.

try this and add deathregions

The "lava" has nothing to do with how to add water.