Puck counted on a third gargoyle offering to house a spirit. So he can trick them all into not realizing the Evil One wasn't in Coldstone but a living vessel.
It's not stated where Xanatos and Fox went during the episode, but an Illuminati meeting is very likely.
Alexander is smarter than a newborn baby should be. Thanks to his magical heritage, he can share the intelligence and consciousness of another if they are used as his vessel.
You can tell the Goliath and Hudson who find Coldstone are fakes right away. Goliath's tone is too happy and Hudson NEVER gives a big happy smile.
The Evil One and Coldstone's mate their new robotic vessels' monikers as their names.