Cheapest priced copy (Tenth Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Kraken's Eye 
Artifact · Uncommon · Magic 2011 · #210
Whenever a player casts a blue spell, you may gain 1 life.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
9 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Tenth Edition | 329 | Uncommon | $0.35 | $0.49 |
| Ninth Edition | 302 | Uncommon | $0.35 | — |
| Ninth Edition | 302★ | Uncommon | — | $0.49 |
| Duels of the Planeswalkers | 93 | Uncommon | $0.35 | — |
| Darksteel | 126 | Uncommon | $0.35 | $0.49 |
| Magic 2010 | 213 | Uncommon | $0.35 | $0.49 |
| Magic 2011 | 210 | Uncommon | $0.35 | $0.49 |
| Magic 2012 | 211 | Uncommon | $0.35 | $0.49 |
| Salvat 2011 | 192 | Uncommon | — | — |
2 rulings from Wizards of the Coast
- 1 October 2009If a player casts a blue spell, Kraken’s Eye’s ability triggers and is put on the stack on top of that spell. Kraken’s Eye’s ability will resolve (causing you to gain 1 life) before the spell does.
- 1 October 2009The ability triggers whenever any player, not just you, casts a blue spell.