Cheapest priced copy (Fifth Edition): $0.35 at Card Kingdom, near mint, their price list as of .
Seasinger 
Creature — Merfolk · 0/1 · Uncommon · Fifth Edition · #121
When you control no Islands, sacrifice this creature.
You may choose not to untap this creature during your untap step.
{T}: Gain control of target creature whose controller controls an Island for as long as you control this creature and this creature remains tapped.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.35 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fifth Edition | 121 | Uncommon | $0.35 | — |
| Fallen Empires | 25 | Uncommon | $0.35 | — |
3 rulings from Wizards of the Coast
- 4 October 2004You do not lose control of the stolen creature if it stops being a creature. You only lose control if Seasinger leaves your control or becomes untapped.
- 16 September 2007Whether you control Seasinger is checked continually, starting when the ability is activated. If, before the ability resolves, there’s any point at which you don’t control Seasinger, the ability has no effect — even if you control Seasinger again by the time the ability resolves. The same is true regarding whether Seasinger remains tapped.
- 16 September 2007If a creature’s controller doesn’t control an Island, that creature is an illegal target. Whether that player controls an Island is checked both when Seasinger’s ability is activated and when it resolves. However, targeting restrictions aren’t checked continually while a spell or ability is on the stack.