The Shadow-Verse is a dark empty pocket dimension Darkwing II has access to. It is a dimension where even Darkwing does not dare to stay at for long. It would appear that some unknown, hostile creatures inhabit the Shadow-Verse.
Background[]
The origins to how the Shadow-Verse came to be is largely unknown, but it is a presumably infinite dark empty abyss outside of Midnight City that is stated by Darkwing II to contain "dark, hungry" things that live in the dimension. It is unknown how the Darkwing II has access to the Shadow-Verse, but likely that the ability was inherited by the original Darkwing to his assistant.

Darkwing II traps Invincible in the Shadowverse.
During the battle between Darkwing II & Invincible, Darkwing II throws Invincible into the pocket dimension, telling Invincible that he will stay in the realm forever. Mark responds that the original Darkwing was better, which prompts Darkwing to go back into the dimension & tell Invincible that he’s the hero who's protecting people from Omni-Man's son. This makes Invincible grab Darkwing II before he escaped, & Invincible restrains him. They both hear an alien roar from the distance that got Mark to threaten Darkwing II that he will feed him to that monster, which made the second Darkwing afraid, telling Mark he would not do it, but Mark reminded him that he’s Omni-Man's son. After hearing another growl from whatever inhabits the Shadow-Verse, Darkwing II lets Mark out, soon after getting karate chopped on the neck, knocking him out. Mark then grabs him & flies off to the Global Defense Agency.

Darkwing sends Lenseless Mark the Shadow Verse.
During the Invincible War, Darkwing II drags Nogogglesible into the Shadowverse to end his assault on Guardians Headquarters. Neither return by the end of the war.
Appearances[]
Season 2 | ||||||||||||
1. "A Lesson For Your Next Life": | Absent | 5. "This Must Come as a Shock": | Absent | |||||||||
2. "In About Six Hours, I Lose My Virginity to a Fish": | Appears | 6. "It's Not That Simple": | Absent | |||||||||
3. "This Missive, This Machination!": | Absent | 7. "I'm Not Going Anywhere": | Absent | |||||||||
4. "It's Been a While": | Absent | 8. "I Thought You Were Stronger": | Absent |
Season 3 | ||||||||||||
1. "You're Not Laughing Now": | Absent | 5. "This Was Supposed To Be Easy": | Absent | |||||||||
2. "A Deal With The Devil": | Absent | 6. "All I Can Say Is I'm Sorry": | Absent | |||||||||
3. "You Want A Real Costume, Right?": | Absent | 7. "What Have I Done?": | Mentioned | |||||||||
4. "You Were My Hero": | Absent | 8. "I Thought You'd Never Shut Up": | Absent |
Trivia[]
- The Shadow-Verse is likely based off DC's Phantom Zone and the Shadow Realm from Yu-Gi-Oh!, considering both have similar names and traits.