A good way to beat the manta ray thing is to hang out under the little hut and spray them when they get close. You'll be protected from the goop and the mantas because they'll go over the hut. Or you could always spin jump and spray. Worked for me.
Also, an easy way to beat "Scrubbing Sirena Beach" is to use the barrels to clean up the major areas. (They're full of water)
