I agree that nightmare could use a buff of some sort, but having said that I'm not big on any of the buff suggestions so far.
Not that they're bad buffs necessarily, but because many of them are adding a new effect to the spell, which would clearly be stronger than the original effect of nightmare.
Deimiotic could work, as could adding a draw effect but most of the options in the poll . . . well . . . I dunno about them
-Fill hand with relics: removes a lot of flavor from the card, wouldn't change balance very much. Removes ghost of time synergy.
-Destroy Light creatures: Not sure how this helps. If you use it on your own critter you don't want to kill it, if you use it on an enemy critter than they can play copies from their hand. Seems almost like a nerf.
-3-5 damage per card: That's a lot of damage (up to 40) and you could play it sooner than you could bolts. Would see more play as a damage-dealer than for it's original purpose.
-Gain
per card: Similar to the damage per card idea, if this was implemented nightmare would become more like immolation than it's current use.
Granted, the effect-per-card options would only work the first time it was used, but can you see NOT using at least one copy of a card that could deal 40 damage for just
?
The other possibility I could think of for buffing the card is if it turned cards in the enemy's hand into the target creature (possibly either all cards in hand or just some of them).