When Hata no Kokoro was first introduced to Hopeless Masquerade, she was declared to have sixty-six masks, but less than ten were shown. These fanworks show what would be unofficial masks if she did have them, usually from other, non-Touhou, series.
For the basic idea, follow the first five examples. Tags are available for her official masks, so don't put them here.
Also, this only applies to famous real-life masks, ones that exist in other copyrighted series, and ones modeled after actual or copyrighted characters. Any masks that do not fit those criteria, such as ones made up by artists or generic-looking masks, do not apply.
Equivalent pixiv tags: こころ他作品仮面