At first i thought Reimu is wearing a smiley bellpepper mask. But after checking the Pixiv page, Her mask is dubbed "正義のにこにこカボチャ仮面" (The smiling Kabocha mask of justice)
HYAWAWAAAAAAAAAAAAH!?OrYeeeeessssss~?Huh? Who's ther-TrickTreat!!Excuse me, lady~And now I'm hungry. While we're at it, I'm taking some of your candy...Fwahahaha! I love the scream of little babies!Give me some candy or I'll pull a prank~...