Everyone and their mother phrase informal
A large number of people
When I went to the cinema last night, everyone and their mother was there.
Everyone and their mother will come to my birthday party tomorrow.
A group of bad or sinful people
To count the number of people in a group to determine who is present
If a person has the devil's own luck, he or she has extremely good luck.
A: Yesterday I won a $10 million lottery jackpot and today I won a car in a draw.
B: You have the devil's own luck.