I grew up reading Oor Wullie at my Scottish granny's house in Fife and it still delivers. There are only a few sites out there dedictated to the bucket-sitting, tacketty-boot wearing, fish supper eating scallywag, but That's Braw is the best of the small bunch. Borrowed from the site is the below explanation of some colloquialisms.
Oor Wullie (and the Broons) are famous for their limited range of memorable exclamations. These are basically corruptions of religious terms... as below.
Jings: derived from Jesus
Crivvens: derived from Christ
Help Ma Boab : derived from help me god or so help me god
Michty Me: derived from Mighty God or Almighty God or God Almighty