Karn, Silver Golem

Text:

Whenever Karn, Silver Golem blocks or becomes blocked, it gets -4/+4 until end of turn.
: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its converted mana cost until end of turn.

Rulings:

• 10/4/2004 The blocking ability triggers only once no matter how many blockers are declared.
• 8/1/2008 A noncreature permanent that turns into a creature can attack, and its <img src="/Handlers/Image.ashx?size=small&amp;name=tap&amp;type=symbol" alt="Tap" align="absbottom" /> 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.