アニメ第138話で初登場。妖怪大辞典によると、ガチン小僧は常に武器なし制限時間なしのガチンコ勝負に挑む妖怪。もはや勝ち負けは関係ない…どれだけ“本気（ガチ）”なのかがなによりも大切なんだ！名前は「ガチンコ」+「小僧」を合わせたものだそうです。
Gachinkozou is a member of the Brave Clan and makes its first appearance in episode 138 of the anime. This yokai loves challenging others to barehanded, no time limit battles. Wins and losses are meaningless to Gachinkozou. The only thing that matters to this yokai is how seriously it can bring its best to every battle. ガチン小僧 Gachinkozou is derived from joining 「ガチンコ」’gachinko‘ which means ‘hardcare/serious competition’ &「小僧」’kozou‘ which means ‘young kid.’
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勝ち負けは関係ない…ガチン小僧 妖怪ウォッチ3アイロンビーズの図案
