Spire Serpent

Oracle Text

Defender

Metalcraft — As long as you control three or more artifacts, Spire Serpent gets +2/+2 and can attack as though it didn't have defender.

Card Rulings

6/1/2011 Spire Serpent still has defender if you control three or more artifacts, although it will be able to attack.
6/1/2011 If Spire Serpent has been declared as an attacker, and you stop controlling three or more artifacts later in combat, Spire Serpent continues being an attacking creature until combat ends.

Additional Information