I came up with an element idea for a mod: SLIM (slime): Moves slowly, greenish colour, pollutes water (turns DSTW into WATR and turns WATR into SLIM), gradually releases GAS, forms from VINE and WATR (I know VINE isn't very stable so to do this you would have to pause the game). PLNT does not grow from slime but VINE does, then turns into PLNT, except for the lower sections. SLIM is flammable and burns at the speed of COAL.
I say that a new element for a mod could be the element SPAM. It could be dark pink absorbs water like sponge but reacts to pressure the same way as goo does.
I was originally going to paste this in the mods section, but I thought it wasn't a mod, it was a suggestion. I wanted this to be an element suggestion for tpt, but they don't want new elements and mod-makers are more accepting. So, it's in the General section.