Karn, Silver Golem

{5} · Legendary Artifact Creature — Golem

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.

Motor: se resuelve a mano

Rulings (2)

A 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.
Wizards of the Coast · 2008-08-01
The blocking ability triggers only once no matter how many blockers are declared.
Wizards of the Coast · 2004-10-04