Ok, you may wonder where I'm going with this, but be patient. Misty's Azurill's mother was Tracey's Marill, right? And Tracey's Marill has been staying at Professor Oak's lab since the end of OI, right? Well, it much have bred with one of Ash's Pokemon, and one of them in either of Marill's egg groups is... Totodile. And Totodile has been shown to be very romantic, and it seems to have a fondness for the Azurill family (Azumarill, remember), and Totodile's male, so that could mean that Totodile bred with Marill and so Azurill is their child.
