Comprehensive Rules pg.17
spot
The word spot sets up a requirement for playing a card or using a special ability in conjunction with a noun such as, "To play, spot an Elf." This is equivalent to, "An Elf must be in play and active for you to play this card."
Cards in your dead pile are active during your turn, but they're not in play. You can't spot a card in your dead pile.
Normally, you don't have to spot all the cards in play that meet the requirement if you don't want to.
If a card says, "for each Elf you spot" and there are 2 Elves in play (and active), you may choose to spot 2 Elves, 1 Elf, or none.
However, if a card says, "you can spot," that means you don't have a choice and you have to spot anything and everything that meets the requirement.
"While you can spot The Balrog, skip the archery phase" means you can't make a choice (it either works or it doesn't).
If the card does NOT say, "you can spot," then you may spot none.