Cheapest priced copy (Shadows over Innistrad): $0.35 at Card Kingdom, near mint, their price list as of .
Uninvited Geist // Unimpeded Trespasser 
Creature — Spirit // Creature — Spirit · 2/2 · Uncommon · Shadows over Innistrad · #94
Skulk (This creature can't be blocked by creatures with greater power.)
When this creature deals combat damage to a player, transform it.
This creature can't be blocked.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Shadows over Innistrad | 94 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 8 April 2016Skulk matters only as blockers are chosen. Modifying either creature's power after blockers are chosen won't cause the attacking creature to become unblocked.
- 8 April 2016If you cause a creature to have 0 power or less, use the actual value (which may be negative) to determine whether it can block or be blocked. A creature with skulk and 0 or less power most likely won't be blocked, but it won't deal combat damage and won't trigger any abilities that trigger when combat damage is dealt.