Heracross first appeared in A Sappy Ending. In the episode, several Heracross and Pinsir were having a territorial dispute. One of the Heracross followed Ash and his friends as they tried to figure out a solution to stop the dispute, which, unsurprisingly, came in the form of Team Rocket. Team Rocket was stopped thanks to the Heracross, and the Pinsir were able to return to their forest, leaving the Butterfree and Heracross. However, the same Heracross was still intrigued by Ash and followed him for a little ways out of the forest. Eventually, Ash saw it following and the Heracross happily allowed itself to be captured.
Heracross dodges Blade's attack.
Heracross' battle debut came in Roll On, Pokémon! where it battled one of Rochelle's Donphan, easily outclassing it before the battle was interrupted. Although it lost a subsequent battle to her most experienced Donphan, Ash was satisfied that it had gained significant battle experience. It scored a significant victory over Blade, Shingo's Scizor, in Wired for Battle!. Although it had trouble initially, with its Leer attack ineffective when Blade used Quick Attack, and then held in the air by its horn, Heracross' reaction time of 0.18 allowed it to pry out of Scizor's claws and then land a damaging Horn Attack. When Blade used Agility, Heracross sat and waited, forcing Shingo to choose between his laptop data and watching the battle. Eventually, Heracross managed to anticipate Blade and hit hard with Fury Attack. Shingo abandoned his laptop and began to order Blade's battle, where the two proved to be very powerful. However, Heracross managed to dodge Blade's Quick Attack, knocked it off balance when it attempted a False Swipe, and finished Blade off with Horn Attack.
Heracross was sent to Professor Oak's lab in Tricks of the Trade in exchange for one of Ash's Tauros. Ash sent Tauros back in the following episode, The Fire-ing Squad, but Professor Oak informed Ash that he wanted to study Heracross's behavior further. Ash agreed to allow Heracross to remain primarily at Oak's lab. It made an appearance in Bulbasaur...the Ambassador!, where it was happy to see Bulbasaur (and more happy to see its bulb) at Oak's lab.
Defeating Magmar with Megahorn
Since then Heracross, like Snorlax, has been called on by Ash for use in difficult battles. In the Johto League Silver Conference, Ash used it in the league battle against Gary. Ash sent it out to fight Gary's Nidoqueen, but Gary quickly pulled Nidoqueen for his Magmar. Heracross fought Magmar regardless of the type disadvantage, sending Magmar flying with Fury Attack. Magmar launched a three pronged attack - Fire Blast, a point-blank Flamethrower, and its own body weight from the fall. However, Heracross overcame the flames by beating it away with its wings. It then broke through Magmar's defense with Megahorn, taking out the Spitfire Pokémon. However, Blastoise proved to be a harder challenge, firing a Hydro Pump powerful enough to blow away Heracross' rock cover and take it out of the battle.
In the special episodes, Heracross made a cameo appearance telling the other Pokémon about Cassidy and Butch.
Advanced Generation series
It appeared in The Right Place and the Right Mime where it met and shook hands with Grovyle.
In Ka Boom with a View!, Ash used Heracross again in the battle against Palace Maven Spenser. Upon being sent out, Heracross immediately went to eat the sap on Spenser's Venusaur. It managed to knock aside the Razor Leaf with Horn Attack, before it was knocked back by a Vine Whip. The two Pokémon rammed into each other with Tackle, both proving to be extremely powerful physically. Heracross struck hard with a Megahorn, then took advantage of the SolarBeam charge-up time to hit again. However, SolarBeam then struck Heracross, knocking it out.
Diamond & Pearl series
Heracross reappeared in An Old Family Blend!, where it was intended to be sent to Ash. However, Cyndaquil was sent instead. It did join Ash for the Lily of the Valley Conference, where it was used for Ash's battle with Nando in League Unleashed!. It was put up against Nando's Kricketune, and sent flying by Silver Wind. Kricketune then used Sing to put Heracross to sleep. However, while asleep, it was able to dodge Kricketune's Fury Cutter attack, because of the newly learned Sleep Talk attack, and combine it with an also newly learned Focus Punch. After it woke up, it had a fierce clash with Kricketune, which Heracross ended with a powerful Megahorn/Horn Attack combo, just before Kricketune attempted another Sing. After the battle, Heracross showed its affection towards Ash by "sucking on" his head.
In The Semi-Final Frontier!, it was the first Pokémon to battle Tobias in the semi-finals of the Lily of the Valley Conference. It seemed to be an excellent choice, with a double type advantage over the Dark type and a recently learned Hyper Beam, which collided with Darkrai's Ice Beam. It tried to attack Darkrai with Horn Attack but was put to sleep by Dark Void. Due to Sleep Talk, it was able to hit the legendary Pokémon with a Megahorn, only to be defeated when Darkrai used Dream Eater, which allowed Darkrai to recover some damage dealt by Heracross.
Best Wishes series
Heracross was reunited with Ash in The Dream Continues!, where it and the rest of Ash's Pokémon posed in a group photo with him.
Heracross eating Bulbasaur's sap
Heracross is an eager but easily distracted Pokémon, especially regarding sap. This was shown in Fighting Flyer with Fire, where Meowth dropped a jar of sap to allow Team Rocket to escape with Pikachu. It also likes to suck sap from plants or trees, as well as Bulbasaur's bulb whenever the two are together, annoying Bulbasaur enough to use Vine Whip to push it away. Again, this is distracting for it, as in Chikorita's Big Upset when it went for Bulbasaur's bulb before helping to rescue Chikorita. Heracross doesn't appear to care how much this annoys Bulbasaur.
Despite these minor flaws, it is a powerful battler, and also extremely strong physically, capable of throwing Team Rocket's tank into the air in A Shadow of a Drought.