Normal Gem is an item that some pokemon use to receive the unburden boost and others use to increase the power of Self Destruct or Explosion. Hitmonlee is the most notable for Normal Gem/Fake Out and Lickilicky is the most notable for Normal Gem/Explosion. Before you go saying they are bad pokemon (because you've said it before), they serve the purpose they are meant to serve. Being on Serebii, you must also remember that not everyone plays just OU. They play UU, RU, NU, PU, VGC and/or non standard rules. What is not allowed in OU or not viable works in other formats/tiers. Do not tell someone something is bad or not allowed because things work. Or for simplicity, it may be their favorite pokemon and they want to use it.