Cheapest priced copy (Kaladesh): $0.35 at Card Kingdom, near mint, their price list as of .
Spireside Infiltrator 
Creature — Human Rogue · 3/2 · Common · Kaladesh · #133
Whenever this creature becomes tapped, it deals 1 damage to each opponent.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Kaladesh | 133 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 20 September 2016For the ability to trigger, Spireside Infiltrator has to actually change from untapped to tapped. If an effect attempts to tap it, but it was already tapped at the time, this ability won't trigger.
- 20 September 2016This is a triggered ability, not an activated ability. It doesn't allow you to tap Spireside Infiltrator whenever you want; rather, you need some other way of tapping it, such as by attacking.