The Jabberwock appears in Forspoken during a Breakstorm event through a boss encounter called a Nightmare, sending hordes of enemies against the player while chaos erupts in Athia's environment. This in-game event provides players with perhaps their biggest challenge, as these Nightmares are challenging opponents that show up occasionally in certain regions to serve as mini-bosses that can be defeated for special rewards. Players will have to manage their wide variety of movement, offensive, and defensive magics to find which spells work best against The Jabberwock.
https://screenrant.com/forspoken-beat-jabberwock-nightmare-fight/