godan verb (-u), intransitive verb
Emphatic or dramatic way to say 'make a mistake'. Often used in conditional or hypothetical forms (〜えば, 〜と, 〜ったら) to mean 'if I/you make a mistake' or 'should I/you make a mistake'. The prefix まかり adds a nuance of 'should it happen that...' or 'if by any chance...'.
まかり間違えば大変なことになる。
If I make a mistake, it will be a serious matter.
まかり間違
If you blunder, I'll hold you responsible.