Surskit, the Pond Skater Pokemon, was a Bug/Water type introduced in Generation 3. At the time, it was the only Bug/Water type, and up until Gen 7, that was still true. However, once it reached level 22, it could evolve into Masquerain, the Eyeball Pokemon. Masquerain is a Bug/Flying type, which had been repeated with Butterfree, Ledian, and Beautifly. Bug/Water is an interesting type combination, being only weak to Electric, Flying, and Rock. Rock types can be dealt with Water type moves, so its biggest concerns are the other two types. But I’ve never seen anyone use a Surskit competitively; I’ve only seen Masquerain being used competitively. It’s a decent Pokemon, with its Special Attack as its best stat, at 100, and its Attack as its worst stat, at 60. However, Masquerain gets access to a variety of special moves, so its low attack isn’t really a problem. In addition, it gets Intimidate as its regular ability, which can be helpful against physical attackers. Its hidden ability is Unnerve, which isn’t all that useful.
Although Surskit and Masquerain were first introduced in Generation 3, they have been given counterparts in Generation 7: Dewpider and Araquanid. Dewpider, the Water Bubble Pokemon, is a Bug/Water type, making that typing no longer unique to Surskit. It also evolves at level 22 into Araquanid. However, while Surskit changed from Bug/Water to Bug/Flying, Araquanid stays a Bug/Water type. Araquanid is a much more usable Pokemon, although its stats are more unbalanced. Araquanid has its Special Defense as its best stat, at 132, while its Speed is its worst, at 42. Its regular ability is overpowered because it has 3 effects in one. In addition, it is unique to this evolution line. First, Water Bubble halves the damage done by Fire type attacks. Although Dewpider is part Water, it is also part Bug, which means it would take regular damage from a Fire type attack. However, this ability is like Thick Fat in a way because they both halve the damage done by Fire type attacks. However, unlike Thick Fat, Water Bubble does not affect the amount of damage done by Ice type attacks. But if you take into account the fact that Water resists most Ice type attacks, it’s not really a problem anyway. Freeze Dry is the only Ice type move that Araquanid would have to worry about, but with its high special defense, I’d doubt it would do too much damage. Second, this ability doubles the power of its Water type attacks. There’s no other ability that doubles the power of a particular type of move, so this is a first. Finally, this ability is exactly like the ability Water Veil. Both of these abilities prevent burns. This is important for Araquanid because its Special Attack stat is half of what its Attack stat is. Araquanid’s hidden ability is Water Absorb, but that’s not nearly as useful because it would take half damage from Water type moves anyway.
Taking all of this into account, which one is better to use in Alola? I won’t be taking into account how they would do in a battle against Hala as an Island Kahuna because the earliest you can get Surskit or Dewpider is on Akala Island. So against Olivia, Araquanid would be better. Although both of them are Bug types, Masquerain takes 4 times damage from Rock type attacks while Araquanid only takes 2 times damage. Plus, Araquanid’s Water typing gives it an advantage over Olivia, so it gets 1 point.
Against Nanu, they’re pretty much the same.
Against Hapu, Araquanid has an advantage over her Ground type Pokemon while Masquerain does not. Yes, Masquerain would be immune to all of her Ground type attacks, but Araquanid takes half damage from Ground type moves anyway. It gets 1 point.
Against Hala, Masquerain would have a clear advantage. Being a Bug and a Flying type gives it 4 times resistance to Fighting type attacks. Plus, its Fighting is weak to Flying, so that’s good as well. Although Araquanid resists Fighting type moves as well, it doesn’t do it nearly as well as Masquerain does, plus neither Bug nor Water do super effective damage against Fighting type Pokemon. It gets 1 point.
Araquanid gets an addition point for Olivia in the Elite Four.
Against Acerola and Kahili, they’re pretty much the same.
Against Kukui, Masquerain has an advantage over Decidueye and Primarina, so it gets 2 points. Araquanid has an advantage over Lycanroc, Ninetales, Magnezone, and Incineroar, so it gets 4 points. Clearly the winner is Araquanid. But that doesn’t mean Masquerain is a bad Pokemon. Masquerain has 2 double resistances: Fighting and Grass. It has an immunity to Ground type attacks, and its Special Attack is pretty good as well. And put in a battle between each other, Masquerain would have the obvious advantage.