From 11:00PM PDT on Friday, July 1 until 5:00AM PDT on Saturday, July 2, the Shmoop engineering elves will be making tweaks and improvements to the site. That means Shmoop will be unavailable for use during that time. Thanks for your patience!
We don't hear much about Echidna in this story, except that she is Chimera's mommy. She disguises herself as a human and rides the elevator with Percy, Grover, and Annabeth to the observation deck of the Gateway Arch. There, she unleashes her pet Chihuahua on Percy. The Chihuahua morphs into Chimera.