From the Super Mario Wiki
Mario rescues a Mushroom Retainer in Super Mario Bros..
“Thank you Mario! But our princess is in another castle!”
—Mushroom Retainer, Super Mario Bros.
Mushroom Retainers are advisers to the leader of the Mushroom Kingdom. The most famous Mushroom Retainer is Toad. Mushroom Retainers assist Princess Peach in her administrative duties of the country. They first appear in Super Mario Bros., where they are kidnapped along with the Princess by Bowser. One Mushroom Retainer appears at the end of each castle and thank Mario or Luigi for rescuing him. However, each one infamously states that the princess is in another castle. In Super Mario Bros.: The Lost Levels, the Mushroom Retainers keep the same role; however, there are more of them to save in this game. In the Super Mario All-Stars versions, more than one Mushroom Retainer can be saved at the same time after beating a castle (however, the number of Mushroom Retainers that can be saved depends on the world that Mario or Luigi is in).
Mushroom Retainers along with Mario and the Chancellor in Super Mario RPG: Legend of the Seven Stars
Mushroom Retainers also appear in Super Mario RPG: Legend of the Seven Stars. In this game, there are six retainers (with Toad being one of them). These Mushroom Retainers serve the Chancellor of the Mushroom Kingdom, as he is in charge of the kingdom until Peach returns. Since this game, the Mushroom Retainers have yet to make a returning appearance (with Toad being the only confirmed Mushroom Retainer who still makes an appearance within the games). However, it is likely that the Toad servants and guards of Princess Peach's Castle have taken over the roles of the Mushroom Retainers.
Mushroom Retainers (along with Toad himself) also make their appearance in Super Mario 3D Land, where they are kept in hostility by some False Bowsers. While they assume the same roles as their initial appearance, they are simply named as "Toads" as opposed to "Mushroom Retainers" similar to Japanese versions.
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