Automatic Recruits

After rescuing Magnemite, it'll turn down the offer to join your Rescue Team. However, after you speak to Wigglytuff and get Rescue Team Camps, it will finally decide to join you

Magnemite Level 7

Rare Skill Ability: Sturdy

After defeating Articuno, Absol will step in and help defend you against the accusations of you causing the problems in the world. It will decide to join your team in order to help prove it

Absol Level 28

Rare Skill Squeeze Out Ability: Super Luck

After completing the main story, you will find a Rescue Mission from Smeargle on the board by Pelipper's post office. If you accept, you'll be able to go rescue Smeargle in Howling Forest. If you succeed, you'll find out that it was hiding from its fellow Smeargle as it didn't want to partake in a ritual. It will eventually decide to join your team. It also has the ability to change the flag at your Rescue Base

Smeargle Level 25

Rare Skill Ability: Own Tempo

After visiting Solar Cave and purchasing the Southern Island camp area, when you return to Pokémon Square, you'll learn of a robbery at Kecleon's shop and that they went towards the Northern Range. Follow them into the dungeon and at the end you'll find Latios who you have to battle. Defeat it and it'll mention its sister, Latias is stuck in the Pitfall Valley. Go to the dungeon and rescue Latias and they will both join you and give you the Southern Island

Latias Level 35

Rare Skill Shared Happiness Ability: Levitate

After visiting Solar Cave and purchasing the Southern Island camp area, when you return to Pokémon Square, you'll learn of a robbery at Kecleon's shop and that they went towards the Northern Range. Follow them into the dungeon and at the end you'll find Latios who you have to battle. Defeat it and it'll mention its sister, Latias is stuck in the Pitfall Valley. Go to the dungeon and rescue Latias and they will both join you and give you the Southern Island

Latios Level 35

Rare Skill Mind Over Matter Ability: Levitate

Throughout the game, a Gardevoir will appear in your dreams. This Gardevoir was the partner of a human that got turned into a Pokémon but eventually fell to a curse.
During the post-game, you'll encounter Medicham & Ekans talking about how Gengar has disappeared. Eventually you'll find Gengar turn up to your base and ask for your help. It first asks you to take him to see Ninetales where you learn that Gengar was the original human that turned into a Pokémon and gives Gengar the Nine-tail Crest to help restore the curse on Gardevoir. Gengar wants to rescue Gardevoir and so asks for your help to rescue it from its curse. Go to the end of the dungeon and help Gengar and the curse will get lifted. Afterwards, Gardevoir has no memory of Gengar and requests to join your Rescue Team

Gardevoir Level 50

Rare Skill Lonely Courage Ability: Synchronize