This is the card holder helmet attachment from Halo infinite, modeled for the Cavallino helmet designed by Moesizzlac on Thingiverse.

https://www.thingiverse.com/thing:4960835

I printed both the helmet and attachment at 100% scale so whatever scale you print the helmet is what you'll want to print the attachment at as well.

I printed it standing up with no supports at 10% infill and it came out great.