OSMO is a fun education set of apps for iPad that help blur the lines between physical and digical world, designed for children 5-12 yo (https://www.playosmo.com/)
But if you lost the tiny red reflector that sits on top of the iPad, you can't play anymore. Except if you download and print this file, ready for you to use with any 1mm or 2mm thick mirror. Any size would do, at least 2cm x 2cm.
It prints just fine at low resolution with any PLA, either version would take 10' and 2g (say around £0.05-0.05€)
NB: you shouldn't use this to avoid buying the game in the first place, knowing that the iPad apps are free to download from the Appstore, but only if you own the game and need a replacement - just saying.