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.
Large Figure Weapon, Claw, Triple, Small with Axle HolePearl Light GrayPart 61806Element 4525717×2
Trans-Clear
2 pieces
Large Figure Wing, with Hologram PrintTrans-ClearPart 61798Element 4655093 or 4532168×2
Trans-Neon Orange
2 pieces
Technic Tooth 1 x 3 with Axle Hole [Rounded Underside]Trans-Neon OrangePart 41669Element 6111281 or 4163574×2
Trans-Red
1 piece
Launcher, Large Figure Weapon, Mistika Nynrah Ghost Blaster Air PumpTrans-RedPart 61810Element 4535379×1
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.