Is given an image:


Googling 'Mata Nui', we discover that it is a reference to the universe of bionicles and its language (Matoran).:


Using the given alphabetical table we can translate the flag

# FLAG
X-MAS{MATANUIHASPREPAREDTHECOOKIES}

Original writeup (https://github.com/Internaut401/CTF_Writeup/blob/master/2019/X-MAS%20CTF%202019/Mata%20Nui's%20Cookies.md).