Spire Serpent
Creature — Serpent
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.
A mirror to draw its eye, a rod to rouse its rage, and a sword to break its bonds.
Johann Bodin
Rulings
Spire Serpent still has defender if you control three or more artifacts, although it will be able to attack.
(wotc • 2011-06-01)
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.
(wotc • 2011-06-01)
Rulings
Spire Serpent still has defender if you control three or more artifacts, although it will be able to attack.
(wotc • 2011-06-01)
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.
(wotc • 2011-06-01)