Ghost & Flying. I believe that's it! Not dark or bug because although they're super-effective against Psychic, they are not-effective against Fighting. And not Psychic, because though it's super-effective against Fighting, it's not-effective against Psychic.
electric and ice are effective against flying
Azelf is a legendary Pokemon.
Water and Grass attacks are super effective against Onix.
Dragon types are gods, nothing is effective against dragon
Ghost & Flying. I believe that's it! Not dark or bug because although they're super-effective against Psychic, they are not-effective against Fighting. And not Psychic, because though it's super-effective against Fighting, it's not-effective against Psychic.
Metronidazole is not effective against the step throat.
electric and ice are effective against flying
Azelf is a legendary Pokemon.
fire: effective against: steel, grass, bug, ice Weak against: Dragon, water, fire, rock Water: Effective against: rock, ground, fire Weak against: water, grass, ice, dragon Grass: Effective against: water, ground, rock Weak against: grass, fire Dark: Effective against: ghost, psychic Weak against: dark, fighting, rock, steel Fighting: Effective against: dark, steel, normal, ice, rock Weak against: bug, poison, flying, psychic Not-Affected: ghost Electric: Effective against: flying, water Weak against: dragon, grass, electric Not-Affected: rock, ground Ground: Effective against: poison, steel, electric, fire, rock Weak against: bug, grass Not-Affected: flying Flying: Effective against: grass, fighting, bug Weak against: electric, steel, rock Poison: Effective against: grass Weak against: ghost, rock, ground, poison Not-Affected: Steel Dragon: Effective against: dragon Weak against: steel Steel: Effective against: rock, ice Weak against: electric, water, fire, steel Ice: Effective against: grass, rock, flying, dragon, ground Weak against: water, steel, ice, fire Rock: Effective against: flying, fire, bug, ice Weak against: rock, ground, fighting, steel Ghost: Effective against: ghost psychic Weak against: dark, steel Not-Affected: normal Bug: Effective against: dark, psychic, grass Weak against: fighting, steel, fire, flying, ghost, poison Psychic: Effective against: fighting, poison Weak against: psychic, steel Not-Affected: dark
Dragon Pokemon are effective against other Dragon Pokemon.
fire is regularly effective against ghost types
Flying and Psychic are super effective against fighting
Lightning is super effective against Water and Flying types in Pokémon battles.
Water and Grass attacks are super effective against Onix.
Bring Pokemon that are faster than Azelf with Paralyze status moves or Sleep status moves, because Azelf's Uproar will keep it awake. Azelf is weak against Dark, Bug, and Ghost type Pokemon, so bring one of them. I recommend Ghost and Dark though, because Ghost isn't affected by Uproar and Dark isn't affected by Future Sight I think. And bring lots of Dusk Balls, Timer Balls, and Ultra balls, because it can be a long battle. Make sure that Azelf is either asleep or paralyzed so it would improve the catch rate. Hurt it until it's health is around red or yellow. Do this rhythm too. 3x Ultras Balls then 1x Timer Ball. Keep doing this. You eventually catch it. Also if you do bring Ghost and Dark type Pokemon, make sure it has the weakest super effective move with them. For example: Astonish: Power 30 and it is super effective.
azelf is at route 23