The Phantom Knights of Cursed Javelin

2 Level 2 monsters You can detach 1 Xyz Material from this card, then target 1 face-up monster your opponent controls; until the end of this turn, change its ATK to 0, also it has its effects negated. This effect can be activated during either player's turn, if this card has a "The Phantom Knights" card as Xyz Material. You can only use this effect of "The Phantom Knights of Cursed Javelin" once per turn.