Green’s Dictionary of Slang

(Aus.) joc. reverse of Christ almighty! under Christ n.

1941		Baker Popular Dict. Aus. Sl.
c.1943		S .J. Baker Aus. Vulgarisms [t/s] 11: myst all critey: Transposed euphemism for Christ Almighty.
1951		D. Stivens Jimmy Brockett 54: Mystall Crikey, it’s good to see you!
1955		in N. Pulliam I Travelled a Lonely Land (1957) 208: Myst all critey! Man’s a dingo’d go out for that sorta thing.