Cheapest priced copy (Eventide): $0.35 at Card Kingdom, near mint, their price list as of .
Dream Thief 
Creature — Faerie Rogue · 2/1 · Common · Eventide · #20
Flying
When this creature enters, draw a card if you've cast another blue spell this turn.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Eventide | 20 | Common | $0.35 | $1.99 |
2 rulings from Wizards of the Coast
- 1 August 2008Although Dream Thief says it looks for "another blue spell," there's no requirement that Dream Thief actually be cast as a spell (or be blue) for this part of its ability to work. For example, if a spell such as Zombify puts Dream Thief directly onto the battlefield, its ability will still check whether you've cast a blue spell this turn, even though you didn't cast Dream Thief itself as a spell.
- 1 August 2008Dream Thief doesn't check whether you've cast another blue spell until its "enters" ability resolves. If Dream Thief's "enters" ability triggers, then you cast a blue instant spell in response, you'll get the bonus.