Doom 64 for Doom II
While retaining the original monsters of Doom II, minus the Icon of Sin and the Spider Mastermind, the mod adds the nightmare imp utilizing the fuzz effect of the spectre with the cacodemon's projectile attack. In addition, the Mother Demon, which combines aspects of both revenant and arch-vile attacks, replaces the Spider Mastermind and is the modification's final boss. Exclusive to Co-op play is the Doom 64 TC-inspired Nightmare Cacodemon, replacing the duplicate bloody mess decoration, who similarly to the nightmare imp is partially invisible, fires three projectiles at a time, and is slightly faster and is stunned less than its regular counterpart.
While all the levels of the original Doom 64 have been recreated, their order has been rearranged due to engine limitations. This includes the game's "fun levels" being included as regular maps.