Psychic-type Pokemon were some of the strongest from Kanto, and some even stronger ones were discovered in Johto.
Generation II added Dark-type Pokemon to the mix, in order to balance out the incredible power of Psychic-types. That still didn't stop Psychic-types from absolutely decimating the other types in the series.
A handful of additions to the Psychic-type category became popular very quickly once players could journey through Johto. Those Pokemon are still very popular to this day, as some of the biggest fan favorite Psychic-types overall.
Note: This article is subjective and reflects the opinion of the writer.
3 most popular Psychic Pokemon from Johto
#3 - Wobbuffet
Wobbuffet is a strange Pokemon. In battle and in the anime series, Wobbuffet can be extremely annoying. That has given it an odd place in the hearts of many fans. Wobbuffet and everything about it is just plain weird.
It has an insanely high 190 base HP stat. That allows it to stay on the battlefield and set up or dish out damage with Counter. The usefulness, and Jessie's Wobbuffet, in the anime boosted its popularity as a Pokemon.
#2 - Celebi
Celebi was popular the minute it was revealed. Fans absolutely adored Mew in Generation I. In Generation II, they were given another small, cute Mythical Pokemon in the form of Celebi.
The anime and movies that showcased Celebi pushed it to the forefront of the series numerous times. It was also revealed to be playing a part in the upcoming New Pokemon Snap. Celebi's popularity has never faltered.
#1 - Lugia
Lugia's popularity came in the same way that Celebi's did. It was given a chance to shine in movies, alongside the Legendary bird trio of Kanto. It also received a spot on a game cover, having been the mascot of Pokemon Silver and SoulSilver.
Even recently, it played a major part in an episode of Pokemon Journeys: The Series. The guardian of the seas is an extremely powerful Psychic-type Legendary that has maintained its popularity for quite some time.