Golem is weak against Grass, Water, and Fightibg. Can be covered by Charizard and Blastoise.
Blastoise is weak against Grass and Electric. Can be covered by Charizard and Golem.
Charizard is weak against Electric, Water, and Rock. Can be covered by Golem, Electrode, and Blastoise.
Electrode is weak against Ground. Can be covered by Blastoise.
Gengar is weak against Dark and Ghost. Can be covered by himself.
Dark and Fightning are weak against Bug and Fightning (dark), and Psychic and Flying. Fightning can be covered by Charizard with his flying types moved if he knows any. Suggestively a Bug or Fightning type POkemon such as a Machamp, Butterfree, or Beedrill.