Very simple cart that drags pixels down, creating some interesting fluid looking shapes towards the end of the process.

Here's a tweet of this running against a non-random screen setup, resulting some really pleasing images.

Cartridge code (176 chars):

for x=0,127 do
    for y=0,127 do
        pset(x,y,rnd(15))
    end
end
::웃::
for x=0,127 do
    for y=0,127 do
        pset(x,y,pget(x+rnd(2)-1,y-1+rnd(2)))
    end
end
goto 웃