Slime Rancher

First set up a pond on your ranch on an empty plot for 450 newbucks. This is where you will keep puddle slimes for their plorts, so locate one (or more) puddle slime(s) (they hang out in shallow spots of water, the ones that dont kill you if you fall in) and drop off in the pond, this counts as 1/5.
Next all you need to do is get one of 4 different types of any slime (pink, rock, phosphor, honey, etc) and quickly drop them into the pond along with the water slime, achievement pops immediatley once they are all inside the pond.
Make sure the pond is located on the ranch because in my experience having a plot on the docks or other farther away areas doesnt count as the ranch (had to move my fruit gardens from the docks to the overgrowth for fruit cocktail to unlock)

Update: multiple users report that placing a pond on a plot works for this in the docks, thanks tommy gun crg and aussiebigfoot

Hey all, quick video on how to grab the achievement Pool Party. Hope it helps!