Needed for Unwelcome Guests. Head into second entrance (coming from newbie area) of Shroomba Caves. Hug left wall making each left turn. Young Shrumblers located (-138, -46, -201) I believe they are elsewhere as well, however, at this point hug the right wall making each right turn.
Head back into first entrance. stop as soon as you see the Large Shrumblers and release the young ones.