Crown of Empires
Artifact
, 
: Tap target creature. Gain control of that creature instead if you control artifacts named Scepter of Empires and Throne of Empires.
"With this crown, assert your authority." —Crown inscription
John Avon
The List (PLST)
• #M12-203Rulings
If any of the named cards stops being an artifact, it won’t be considered by these abilities.
(wotc • 2011-09-22)
Whether or not you control the correct artifacts is determined when the ability resolves.
(wotc • 2011-09-22)
If you control artifacts named Scepter of Empires and Throne of Empires, the targeted creature won’t be tapped. You’ll just gain control of it.
(wotc • 2011-09-22)
Rulings
If any of the named cards stops being an artifact, it won’t be considered by these abilities.
(wotc • 2011-09-22)
Whether or not you control the correct artifacts is determined when the ability resolves.
(wotc • 2011-09-22)
If you control artifacts named Scepter of Empires and Throne of Empires, the targeted creature won’t be tapped. You’ll just gain control of it.
(wotc • 2011-09-22)