Cheapest priced copy (Lorwyn): $0.35 at Card Kingdom, near mint, their price list as of .
Judge of Currents 
Creature — Merfolk Wizard · 1/1 · Common · Lorwyn · #22
Whenever a Merfolk you control becomes tapped, you may gain 1 life.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Lorwyn | 22 | Common | $0.35 | $1.99 |
2 rulings from Wizards of the Coast
- 1 October 2007This is a triggered ability, not an activated ability. It doesn’t allow you to tap the creature whenever you want; rather, you need some other way of tapping it, such as by attacking with the creature.
- 1 October 2007For the ability to trigger, the creature has to actually change from untapped to tapped. If an effect attempts to tap the creature, but it was already tapped at the time, this ability won’t trigger.