Below is a list of all the costumes for Sylvando in Dragon Quest XI S.
The first costume you can get for Sylvando requires finding an in-game recipe, called The Dapper Chap. This recipe is given to you as a reward for completing Quest 12 - Skincare for the Fierce and Fabulous. In order to forge both items needed for the costume, you will need Silkblossom (x3), a Magic Beast Hide, a Green Eye, a Glimmergrass, and a Celestial Skein.
The Parade Participant
This costume is gotten as part of the main story, in the middle portion of the game. Thus, you don’t have to do anything special to get it.
The Parade Master
This costume is exclusive to the Definitive Edition version of the game and there are two ways to get it. The easier way is done during Sylvando’s Interlude, where he will be able to recruit a number of NPCs for his band. If you recruit all of the NPCs, then he will have this costume upon joining back up during the second part. If you do not recruit all of the NPCs, then you will be able to trade for it at the Octagonia Casino.
You will have to find the recipe, called Glam Gear for Go-Getters, for this costume. You will obtain the recipe for completing Quest 28 - Madame Labouche’s Life Lesson. In order to forge both items for the costume, you will need the following items: Gold Ore (x2), Royal Ruby (x3), Belle Cap (x2), Slipweed (x2), Lamsbwool (x2), and Love Potion (x6). The Love Potion item can be traded for at the Octagonia Casino.
Once you reach the final part of the game, you will be able to do an event in Puerto Valor that opens up the final bit of Sylvando’s skill tree. After finishing that event, return to Puerto Valor and speak to Servantes in Don Rodrigo’s house to receive the Coraza de Cabalerro piece of equipment and this costume.
Even Suaver Sylv
The two items needed for this costume come from the recipe, Dress to Impress, which is gotten by speaking to Golden Boy in Octagonia. You will be able to do this after completing the events in the final part of the game in Octagonia. He will be located on the stage in the slots section of the casino. In order to forge the items, you will need the following items: Technicolour Dreamcloth (x2), Serpent Skin (x2), Equable Emerald (x2), a Spectralite, Colourful Cocoon (x2), Buzzberries (x2), Royal Ruby (x2), and Sparkly Sap (x2).
The two items needed for this costume come from the recipe, Glammer Gear for Go-Getters, which is gotten from the Mini Medal Academy upon turning in a total of 90 Mini Medals. Note that you can only get the recipe during the final part of the game. In order to forge the items, you will need the following items: Gold Bar (x2), Spectralite, Lucida Shard (x2), Crimsonite, Narspicious (x3), Serpent Skin (x2), Kaleidocloth (x2), Cherry Blossom Petal (x2), and Love Potion (x6).