Below is a list of all the costumes for Veronica in Dragon Quest XI S.
This costume is exclusive to the Definitive Edition of the game. For the Switch version, you will have to download the Champion’s Pack DLC on the eShop (it’s free), then claim it in-game. Other versions of the Definitive Edition will not have to download anything. To claim it, go to Misc, then Settings, and you will see that option towards the bottom of the list.
The Kitty Cat
Both pieces needed for this costume are available in Gondolia. For the Cat Hat, you can simply purchase it from the armor shop. For the Cat Suit, there are two merchant brothers on the west side of the town, one right beside the entrance and the other up the stairs from him. During the first part of the game, you can haggle the price down for this armor until it reaches 1,000G, which is when you should purchase it. If you miss this opportunity during that part of the game, then you can simply purchase it from the normal armor shop later.
The Spotty Sorceress
This costume will require you to get a recipe (All Good Things), which is gotten by talking to a man in red near the entrance in Puerto Valor (can be done on your first visit). You simply need to speak with the NPC, as you don’t have to do anything else. To forge the items, you will need Faerie Fluff (x3), Waveweed (x2), and a Cottontop.
The Medal Maniac
The Uniforme de l’Academie is a piece of armor that can be equipped to any of the female party members. There are three of these in the game, although in the Definitive Edition, you only need one in order to access the costume on all three characters. In the original version of the game, you will need to equip them on each character to trigger the costume. You get one for turning in 25 Mini Medals, another is behind the Magic Key door in the Mini Medal Academy, and the third is a reward for completing Quest 20 - The Agony and the Ecstasy.
The Goody Two-Shoes
This costume is exclusive to the Definitive Edition of the game. Once you reach the final part of the game, you will head to Havens Above and secure the Ultimate Key from a chest. Next to that chest will be two others, one of which contains the Little Angel’s Frock armor, which triggers this costume.
The Mega Medal Maniac
This costume is exclusive to the Definitive Edition version of the game. The costume is shared across all three female party members, as you only need one of the armors in order to unlock the costume. As you make progress in Tickington, you will unlock an area called Whealbrook. Complete the quest there, then go to Quester’s Rest afterwards, speaking to Sellma behind the counter on the right, to purchase the Uniforme Chic de l’Academie armor.
The Black Cat
This costume is exclusive to the Definitive Edition version of the game. You can purchase both pieces of armor from Sellma in Quester’s Rest. See the costume right above this one to learn how to unlock it.
The Flapping Fairy
In order to unlock this costume, you will need to progress through the game until you reach the final part. Visit Octagonia and complete the event there, then go to the casino. On the one side of the casino (area with the slots), you will find a stage. At one of the tables in front of the stage will be Sinderella and Whambelina. Speak to each of them to get the Stellar Starflower and Stellar Suit items, both of which are needed for the costume.
The High Priestess
You will need to find the recipe in order to forge the two items for this costume, the Crown of Eternity and the Gown of Eternity. The recipe, Eternal Elegance, is located on Level 1 of The Sage’s Trial - Hoarder’s Keep. The materials needed to forge both pieces include Kaleidocloth (x3), Cumulonimbough (x4), Permasnow (x2), Red Wood (x2), Chronocrystal (x4), and Pale Pearl (x3).