A Hardheaded Battle of the Metapod
"Challenge of the Samurai," one of the episodes from Indigo League
Episode 4 has one of the series' most ludicrous battles. Ash's newly developed Caterpie is a Harden-only Metapod.
This bug-using boy calls himself Samurai and challenges Ash. Samurai employs a Metapod after Ash's horribly breaks Pinsir's horn.
The two Metapod cannot damage each other, thus the combat continues until Misty starts sunbathing because of boredom.
The three trainers are forced to retreat as a swarm of Beedrill attacks, culminating the battle.
Without that, Ash's stubbornness may have kept him fighting this impossible struggle, but it's delightfully bizarre.
Ash's Muk Smothers Bellsprout in a Horrific Victory