Alternate costumes
Complete the indicated task to unlock the corresponding costume.
Dangerama: Complete the game, attack Darkdeath three times, and watch the ending.
Etranger: Complete the game and watch the ending.
Firo: Defeat Firo on the tenth floor of the "Baccano!" Dengeki dungeon.
Index: Defeat Index at the bottom floor of the "A Certain Magic Index" Dengeki dungeon.
Taiga Aisaka: Defeat Taiga Aisaka on the tenth floor of the "Toradora!" Dengeki dungeon.
Costumes shop
Talk to the Prinny at the bottom of your secret base quickly and repeatedly. To do this easily, hold Circle and rapidly tap X until the confirmation message appears. The costumes shop and the Etna, Flonne, and Laharl costumes will be unlocked.
G-Darkdeath equipment
Throw the indicated Darkdeath item into the spring that randomly appears inside the dungeon. Note: The spring often appears at Mid-Tier Hero Mastery Cave. You can only use one spring for each piece of equipment, however there is a chance that the item will not be returned.
G-Darkdeath Body: Throw Darkdeath Body into a spring.
G-Darkdeath Head: Throw Darkdeath Head into a spring.
G-Darkdeath Left Arm: Throw Darkdeath Left Arm into a spring.
G-Darkdeath Leg: Throw Darkdeath Leg into a spring.
G-Darkdeath Right Arm: Throw Darkdeath Right Arm into a spring.
Alternate costumes...