Who is Gizmoduck?!

1 Woo-oo! 2 Daytrip of Doom! 3 The Great Dime Chase! 4 The Beagle Birthday Massacre! 5 Terror of the Terra-Firmians! 6 The House of the Lucky Gander! 7 The Infernal Internship of Mark Beaks! 8 The Living Mummies of Toth-Ra! 9 The Impossible Summit of Mt. Neverrest 10 The Spear of Selene! 11 Beware the B.U.D.D.Y. System! 12 The Missing Links of Moorshire! 13 McMystery at McDuck McManor! 14 JAW$! 15 The Golden Lagoon of White Agony Plains! 16 Day of the Only Child! 17 From the Confidential Casefiles of Agent 22! 18 Who is Gizmoduck?! 19 The Other Bin of Scrooge McDuck! 20 Sky Pirates...In the Sky! 21 The Secret(s) of Castle McDuck! 22 The Last Crash of the Sunchaser! 23 The Shadow War