Hillhelm Family: Lil Piggy

Buy Sparkbug Jar use it and then look at these locations. Could be more spawn points, these where all those I could find mentioned in the achievement post.

/way 64.06 25.98
/way 64.5 27.36
/way 64.6 26.04
/way 64.06 25.98
/way 64.75 27.32
/way 63.80 26.43
/way 64.02 25.99
/way 64.77 26.53
/way 64.04 26.02
/way 64.02 25.92
/way 64.75 26.53
/way 63.81 26.48

You need a "Light buff" to find this little one. To get this buff, you’ll need to use one of the following similar items - [item=220756] or [item=225253] or [item=218107].
Then go around /way #2215 63.8 26.5, and he will pop up.

After running around for hours, trying every spot possible with different items [item=218107], [item=220756] and Sentry Flare Launcher I couldn't find the pig.

It turns out mine was hiding between a fence and some bushes at /way 64.75, 26.49 . I used [item=218107].

I hope that helps.