The value of X is determined only once, as the reflexive triggered ability resolves
If a creature you control has been goaded by each of your opponents, the creature must attack an opponent (rather than a planeswalker or battle), but you choose which opponent it attacks
I had a lot more luck selling these before the Deckbuilders Toolkit was created, though, and lately I havent been able to move them at all
Fear of the Dark Four generic, one black enchantment creature Nightmare 5/5 Common Whenever Fear of the Dark attacks, if defending player controls no Glimmer creatures, it gains menace and deathtouch until end of turn
I think this is really strong as you can send out a card you no longer care about, (such as a land) or if you can recur it (such as said land when you control a Ramunap Excavator and you can just replay it)
It's a 4/5 with menace that forces opponents to sacrifices a nontoken creature or planeswalker