Mareanie, the Brutal Star Pokemon, is a new Pokemon that was introduced in Sun and Moon. It can only be found by SOS calls from Corsola. It is a Water/Poison type with the regular abilities Merciless (which makes any attack land as a critical hit if the target is poisoned) and Limber (which prevents paralysis). For its hidden ability, it has Regenerator (which heals at most 1/3 of your HP every time you switch out. It heals less if you have more than 2/3 of your HP). Once it reaches level 38, it evolves into Toxapex. Water/Poison can be a useful typing. It has been around since Generation 1 with Tentacool/Tentacruel. There is also Qwilfish and Skrelp (although Skrelp becomes Dragon/Poison once it evolves). Water has 2 weaknesses: Electric and Grass. Since Poison resists Grass type moves, Water/Poison types take regular damage from Grass type moves. However, getting a Poison typing means it will be weak to Ground and Psychic. Ground types aren’t much of a problem because although Water doesn’t resist Ground, it is super effective against it. Psychic types are a bit more of a problem but it doesn’t resist Water nor Poison. Being a Poison also gives you immunity to poisoning for the most part plus Toxic will always land. This is especially useful for Toxapex’s Merciless, because although it’s more of a wall than an attacker, being able to critical hit your opponent while they take damage from poison can be a good strategy. Since Toxapex is a wall, it can also take hits while your opponent’s HP drops. Regenerator is also a useful ability because it can take a while for your opponent to drop your HP, and being able to recover 1/3 of your health just by switching out can be frustrating. You can poison the opponent, and if your health drops too low you can just switch out. Limber isn’t that good of an ability for Toxapex because Toxapex is a slow Pokemon anyway. Although Mareanie is an annoying Pokemon to get, it has much competitive use.