FOILCheapest priced copy (World Championship Decks 1999): $7.99 at Card Kingdom, near mint, their price list as of .
Karn, Silver Golem 
Legendary Artifact Creature — Golem · 4/4 · Rare · Arena League 1999 · #8
Whenever Karn blocks or becomes blocked, it gets -4/+4 until end of turn.
{1}: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
5 printings · $7.99 to $84.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander's Arsenal Oversized | 6 | Rare | — | $8.49 |
| Arena League 1999 | 8 | Rare | — | $84.99 |
| Urza's Saga | 298 | Rare | $15.99 | — |
| From the Vault: Relics | 6 | Mythic | — | $14.99 |
| World Championship Decks 1999 | kb298 | Rare | $7.99 | — |
2 rulings from Wizards of the Coast
- 4 October 2004The blocking ability triggers only once no matter how many blockers are declared.
- 1 August 2008A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.