Brandon's Dusclops is Brandon's most powerful non legendary Pokémon.
Despite the fact that it had not reached its final stage of evolution, Brandon's Dusclops was incredibly powerful, possibly even rivalling his three Legendary Golems. It first appeared in Gathering the Gang of Four, where it faced off against Ash's Charizard. Dusclops blocked Flamethrower with an incredibly strong Will-O-Wisp and then stopped Charizard from using Steel Wing with Shadow Punch before being hit by DragonBreath. Dusclops then used Mean Look to stop Ash from recalling Charizard and grabbed hold of the Flame Pokémon's wing when he used another Steel Wing. Then Dusclops used Confuse Ray before pounding the helpless Charizard with Shadow Punch and burning him with Will-O-Wisp. Charizard furiously snapped out of confusion and hit Dusclops with a powerful DragonBreath. Dusclops fired another Will-O-Wisp in retaliation and then once again grabbed Charizard's wing when he attempted another Steel Wing. Charizard would have finished Dusclops with Seismic Toss if Dusclops hadn't been a Ghost type. Dusclops escaped from Charizard and finished him with a devastating Shadow Punch.
In Pace - The Final Frontier, Dusclops provided a considerable challenge for Ash's Bulbasaur, despite having been worn out from battling Charizard. It hit Bulbasaur with Shadow Punch and endured Razor Leaf. Then it ducked beneath Vine Whip and landed another Shadow Punch. Bulbasaur managed to land a Leech Seed but somehow Dusclops stayed on its feet, despite all the damage it had taken from Charizard, displaying unbelievable endurance. Then it used the Mean Look and Confuse Ray combination before burning Bulbasaur with Will-O-Wisp. Finally Bulbasaur snapped out of confusion and charged a Solarbeam. The exhausted Dusclops didn't have time to try another Confuse Ray because of the Leech Seed, so it made one last desperate attempt to defeat Bulbasaur with Will-O-Wisp. Bulbasaur leapt over the attack and finally defeated Dusclops with Solarbeam.
+ indicates this Pokémon used this move recently.* - indicates this Pokémon normally can't use this move.
Brandon's Dusclops is the only Pokémon that was not fully evolved to have defeated Ash's Charizard since it evolved from Charmeleon (any battles in which Charizard refused to fight don't count since it was not actually knocked out in those battles).
Dusknoir had not been revealled when Ash battled Brandon which is presumably the writers reason for not having Dusclops in its final evolution stage. It is possible that, if one forgets about the fact that Dusknoir did not exist when Gathering the Gang of Four and Pace - The Final Frontier were first broadcast, Brandon did not have a Reaper Cloth and was therefore unable to evolve Dusclops. Another possibility is that Dusclops simply might not want to evolve and might have a similar veiw towards Dusknoir that Ash's Pikachu has towards Raichu or perhaps it even hated its evolved form like Tyson's Meowth and Team Rocket's Meowth hated all Persian.