Below is a list of all the costumes for Erik in Dragon Quest XI S. The thing with a lot of costumes for Erik is that they have variants for each one. Most of the costumes have one with a headgear on, and a variant with it off.
The Lupine Look
This costume is exclusive to the Switch version of the game and requires downloading the free Champion’s Pack DLC from the eShop. Once you do that, you can redeem the items from the in-game menu to make it available to Erik to wear.
The Swindler/The Spiky Swindler
To gain this costume, you first have to find the recipe for it, which is gotten by completing Quest 15 - Shiver Me Timbers!. To forge both pieces, you will need Faerie Fluff (x4), a Cottontop, a Blue Eye, and Maiden’s Favour (x2).
The Corsair/The Coarse-Haired Corsair
In order to get this costume, you will have to find two separate pieces of equipment. The Corsair’s Cap can drop from Gyldenbritches, but you will always get one from the boss fight in Gyldenhall in the middle part of the game. For the Corsair’s Coat, you will have to defeat Alizarin in the middle part of the game, then you will be able to purchase it from the shop in Nautica (requires you to be a fish).
The Stone-Cold Killer
This costume is exclusive to the Definitive Edition. In the final part of the game, you can visit Insula Centralis and find some flying mounts there. Once you get a mount, flying to the northwest island and you should find a chest with the Assassin’s Attire, the only armor needed for this costume.
The Swindler King/The Spiky Swindler King
Once you reach the final part of the game and obtain the Ultimate Key, go to the Heliodor Sewers to find some locked doors. Behind one of them will be a chest with the recipe, King of the Swindlers, allowing you to craft both pieces needed for this costume. To forge both pieces, you will need Technicolour Dreamcloth (x5), Gold Nuglet, Mythril Ore (x2), Royal Ruby (x2), Savvy Sapphire (x2), and Slipweed (x4).
The Pirate King/The Prickly Pirate King
This set is split into two items that are gotten separately. The first item, the Pirate King’s Cap is gotten as a reward for completing the event in Lonalulu in the final part of the game.
For the other piece, the Pirate King’s Coat, there is a side story in Cobblestone to help out Gemma there. This involves hunting down specific NPCs to send back there. These NPCs are usually behind other events you have to complete. They are as follows:
- Derk on Cobblestone Tor
- Noah in Gondolia
- Underdigger/Abominable Showman in Octagonia
- Jormun in the Hekswood
Once you recruit all of the NPCs above, return to Cobblestone and you can find the Coat in the item shop.