Rule out the usual hiding places first. If the piece really is gone, check the set piece by piece
and leave with the element ID LEGO asks for, or a link to buy the part.
Bar 1L with Clip [Cut Edges and One Side Hole] [Gap in Clip]Dark Bluish GrayPart 48729bElement 6278155 or 45792341 spare in the box×2
Energy Effects
2 pieces
Large Figure Shield, HexagonTrans-Bright GreenPart 98566Element 4652059×2
Projectiles / Launchers
2 pieces
Projectile, Large Figure Weapon, Zamor Sphere / BallFlat SilverPart 54821Element 4655097 or 4609596×1
Launcher, Large Figure Weapon, Zamor Sphere Launcher, Bottom with Axle HoleTrans-Bright GreenPart 98564Element 6021672 or 4652057×1
Technic Connectors
2 pieces
Technic Axle Connector 2 x 3 with Ball Socket, Open Lower Axle HolesBlackPart 93571Element 4610948×2
Technic Pins
2 pieces
Technic Pin with Friction Ridges Lengthwise and Center SlotsBlackPart 2780Element 4121715 or 2780261 spare in the box×2
Tick each piece as you find it, or mark it missing.
When a piece really is missing
Ask LEGO
LEGO takes requests for pieces missing from a new set through its customer service site. The form asks for
the set number and each piece's element ID, the number printed beside the piece in the parts list at the back
of the instructions. This checker lists both.
Mark a piece missing and your list links it to an eBay search for that part, which also covers pieces from
older or second-hand sets.
Keep a record
Copy or download your missing list (the CSV opens in any spreadsheet), or print the whole checklist and tick
pieces off on paper. Your marks stay in this browser, so you can check a big set over several sittings.