I have run into them a couple of times.  I think they are on the underside of whichever planet they are on.  You can see their footprints walking around and if you look away from them they appear.  Then if you move or look at them, they disappear.  Is there anything that you can do to them?  I have tried shooting them to no avail and tried stomping around them or sneaking up on them.  Nothing works.  Does anyone have any ideas? Thanks.

Spin attack works for me, they only give out star bits

Try a shell or a coconut. They give a crapload of star bits.

just follow them, and when you are above then do a spin attack, they are basically bags full of star bits.

just spin attack. They usually give out 19 or 20 star bits depending on which galaxy your on.

ya i just try to trick them and run around them then into them. Then i just spin and kill.

Got it, tried the spin attack and it worked. I do not know why I did not try that before. I guess I thought there was some special thing with them or something. Oh well, thanks guys.

Your welcome! and they look really weird. light green aliens or something.

the easiest way is if you have a partner. Just sit there and wait for him to appear, then get your partner to hold him in place and walk up and whack him.

Oh wow, I forgot to figure that out.  I didn't think you could spin them since they were underground, but I should have realized that considering those big guys...oh well.