The original form of '막요래' is '막 이래'

'막 이래' means like 'Look at what I'm saying!'

When you want to tell something strange or challenging without ruining the atmosphere, by using this word you can avoid the embarrassing situation.

For example, If you say to someone that "Don't you think that I'm more handsome than you?", He might think that you're a little strange. But if you add '막 이래', He may think the word you said is just a joke.