Not only to better protect the card, but also to have the value and authenticity officially established
Usually there are two that are drawn by the same artist
As Duskmourn: House of Horror is based on Betrayal at House on a Hill, a game in which one or more players will betray their party and seek to destroy them (as the opposing players must defeat the betrayer), this slotted perfectly inline with Archenemy's mechanics
For the same reason, I think that makes it harder for old fans of the show/card game to get back into it
Harlequin #163 UR Loading
It has a very relevant creature type, a decent stat line, and evasion, and offers a nice stax effect by putting the brakes on any activated abilities that other players may be counting on