The Pokémon anime has followed the journeys of Ash Ketchum for well over two decades now, spanning eight generations and several different regions. In that time, Ash has made new friends and caught numerous interesting species of Pokémon in a bid to raise them well and have them help him achieve his dreams of becoming a Pokémon Master.
The generic format for each region is to obtain eight Gym Badges from Gyms in order to compete in that region's Pokémon League tournament. Ash has therefore fought countless Gym Leaders over the course of his entire Pokémon journey, finding some battles much easier than others. His initial Kanto adventures are known for frustrating fans, due to the nature of Ash coasting his way through the process, rarely battling his way through and legitimately earning his badges.
8 Team Rocket Battled At The Viridian Gym In Giovanni's Stead
Team Rocket has never been known for their skills in battle, often relying on stealth, disguises, and sneak attacks in carrying out their evil plans, but when Giovanni is called away on urgent business, he entrusts the Viridian Gym to them.
The battle against Ash quickly goes off the rails, with Team Rocket rigging up booby traps to deal damage to the trainers as well, and the 3-on-3 quickly becomes an unruly scuffle when Jessie sends in her own Pokémon in addition to Rhydon, Machamp, and Kingler. Pikachu is able to defeat all of them with a Thunderbolt, and when Team Rocket blasts off, they drop the Earth Badge that happens to fall into Ash's hands.
7 Misty & Ash's Gym Battle Was Messy Before The Team Rocket Interruption
When Ash faces Misty at the Cerulean City Gym, he is only really put at a disadvantage when Pikachu refuses to battle against a friend, prompting Ash to turn to Butterfree and Pidgeotto instead. With the water-based battlefield, Staryu is able to quickly gain the advantage over Butterfree by knocking it into the water, forcing Ash to switch to Pidgeotto.
Misty switches to Starmie, the evolved form of Staryu, but it is immediately overpowered by Pidgeotto and on the verge of defeat, before Team Rocket's interruption. This particular bout never got to be decided, even if the two trainers did end up facing each other again down the line, but Ash received the Cascade Badge regardless.
6 Koga Put Up More Of A Fight In The First Interrupted Battle Than In The Rematch
Koga starts off his Fuchsia Gym defense against Ash with his Venonat immediately evolving into Venomoth, causing instant problems for Pidgeotto and Charmander before Team Rocket interrupts proceedings.
Once Team Rocket has been dealt with, Koga and Ash restart their battle, with it being 1-on-1 this time, pitting Charmander against Golbat. While Venomoth seemed capable of keeping up with Charmander, Golbat is easily swept aside after its initial barrage of tricky attacks, earning Ash his Soul Badge.
5 Brock Was Much Better Than Ash Despite Ash's Boulder Badge Saying Otherwise
Brock is Ash's first gym battle in the anime, with his Onix instantly eliminating Ash's inexperienced Pikachu with a devastating Bind that forces the new trainer to concede defeat. After some training in supercharging Pikachu and its Electric-type capabilities, Ash challenges Brock to a rematch.
Ash pushes his luck, neglecting type matchups by sending out Pidgeotto against Geodude, having Pikachu somehow knock out the Rock Pokémon despite their supposed immunity to Electric-type moves, and finally taking advantage of the sprinklers weakening Onix. Ash fluked his way to getting the Boulder Badge, but Brock should have finished the battle long before the sprinkler mishap.
4 Lt. Surge's Raichu Was Powerful, But Its Lack Of Speed Was Exploited In The Rematch
When Ash first faces off against the Vermillion City Gym Leader Lt. Surge, he is overwhelmed by how much stronger his opponent's Raichu is than his own Pikachu. This humiliation comes from Ash's lack of preparation and refusal to research the Gym Leader before his battle.
In a simple 1-on-1 battle, however, all Ash has to do is focus on overcoming the Raichu and he can claim victory. With help from his friends, Ash discovers that Raichu evolved early and opted for power over speed, allowing Pikachu to exploit this in their rematch. Surge even becomes flustered and desperate, leading to his defeat.
3 Erika Had Ash On The Ropes Before Their Match Was Interrupted
In the Gen I Pokémon games, Erika is often considered to be one of the easier Gym battles, with Grass types having several weaknesses and very few strong offensive moves. Both of these hold true during Ash's battle against her in the anime, with the Fire-type Charmander instantly defeating a disadvantaged Weepinbell, while Erika relies on Tangela's Stun Spore to get past Bulbasaur and Gloom's strong scent to overpower Charmander.
The battle never gets its conclusion, however, due to a classic Team Rocket interruption that sets the Gym on fire, but Ash still gets his badge after saving Gloom from the blaze, despite being on the backfoot during their battle.
2 Blaine Was Strong Enough To Get A Good Fight Out Of Ash's Charizard
In the first bout between Cinnabar Island Gym Leader Blaine and Ash Ketchum, the former's Ninetales and Magmar prove too strong for Ash, as Charizard disobeys and forfeits, while Squirtle loses immediately and Pikachu has to be rescued by its trainer. The rematch, however, is a straight 1-on-1 with Charizard against Magmar.
For one of the first times since evolving from Charmeleon, Charizard deems its opponent worthy enough to take the battle seriously, and the two have an intense bout between Fire types. Charizard eventually does enough damage to emerge victorious, and it is a rare instance of Ash actually winning a battle to earn his Gym Badge.
1 Ash Needed Outside Interference From Haunter To "Defeat" Sabrina
Sabrina has always been regarded as one of Kanto's toughest Gym Leaders in the Pokémon games due to her powerful Psychic Pokémon, and this is also the case in the anime. Ash immediately underestimates a seemingly harmless Abra at the start of their first battle, but Abra quickly uses Teleport, before evolving into the formidable Kadabra. Kadabra is then able to quickly direct Pikachu's own moves back at it to devastating effect, ending the bout in record time.
In their rematch, Pikachu is able to land a hit this time, but Kadabra's use of Recover immediately nullifies any progress made. Ash ends up winning his badge in a contentious manner, with a Haunter making Sabrina laugh for the first time in ages, but he did well to not lose the rematch.