Poison-type Pokemon have always been considered one of the most dangerous typings in the series.
There are quite a few Poison-type Pokemon, and several of them come with a second typing. It started with the likes of Beedrill, Gengar, and Nidoking. They set the bar quite high.
In Hoenn, a few fan favorites from previous Generations were included alongside brand new Poison-types that gained some popularity. The Hoenn region most definitely brought the goods in terms of Poison-type Pokemon.
Note: This article is subjective and reflects the opinion of the writer.
3 most popular Poison Pokemon in Hoenn
#3 - Muk
Grimer could be found on the Fiery Path of Hoenn. Grimer, of course, evolves into Muk. Muk is one of the original 151 Pokemon and is a pretty solid Poison-type. Muk is also quite underrated.
105 HP, 105 Attack, and 100 Special Defense are very good stats. It only has weaknesses to Ground and Psychic. Being an original Pokemon, it was bound to be more popular than some others in Hoenn.
#2 - Crobat
In just about every Generation of Pokemon, Zubat can be found in caves. As annoying as Zubat may be, its evolutions are great. Crobat was introduced in Generation II but is a wonderful Poison/Flying-type for a Hoenn team.
It has insane Speed at a base of 130. The rest of its stats are a bit lower but are fairly balanced. Being faster than most Pokemon sees Crobat given the opportunity to dish out some poisonous damage. Fans absolutely love that.
#1 - Roselia
Roselia was a brand new Grass/Poison-type Pokemon introduced in Generation III's Hoenn region. It immediately gave all other Grass and Poison-types a run for their money. Roselia became popular right off the bat.
Now, it has an evolution in the form of Roserade that is even more popular, but Roselia is amazing all by itself. 100 Special Attack and 80 Special Defense allowed it to withstand hits and dish out many of the most powerful Special Grass-type moves.