The Slimy Little Pile is a very annoying enemy for two reasons: it can make everyone in your party cry, and it can call for another Slimy Little Pile. Thus, by the time you kill it with the atrocious accuracy that crying gives you, it's likely that you'll be fighting several more. On the positive side, they don't do much damage to you, so once you finally defeat them all, you will get a good amount of experience.

If the Slimy Little Pile is with other enemies, use PSI fire to kill them off so they aren't doing any damage to you. Then bash the Slimy Little Pile until you start crying.

Once you start crying, you have two options: use PSI Fire or Freeze and end the battle quickly, or conserve PP and use your now (temporarily inaccurate) standard attacks. The latter may be preferable as you may not have much PP at this point in the game, but be prepared for a long battle. Keep attacking a single Slimy Little Pile until it dies, and if another one has joined the battle by this time, attack it. Use PSI only for Lifeup. Using Healing β to cure the crying is probably a waste of PP, as it is likely that you will start crying again before you can get in enough hits to kill the Slimy Little Pile.