i-adjective
mystifying; puzzling; baffling
Slang adjective used mainly by younger speakers online to describe something confusing or hard to understand. Derived from 謎 (なぞ, 'mystery') + い, turning the noun into an i-adjective.
この問題、まじで謎いんだけど。
This problem is seriously baffling.
あの人の行動はいつも謎い。
That person's behavior is always mystifying.