Azurill to Azumarill: Level up, friendship at 160 or more, then level 18

Stages

Azurill starts a line of three stages, from Generation III

1. Azurill#0298, babynormalfairy
2. Azurill to MarillLevel up, friendship at 160 or more
   Marill#0183waterfairy
3. Marill to AzumarillLevel 18
   Azumarill#0184waterfairy

How each step works

2 steps in the Azurill line, the same in every game that has them

Breeding

Azurill hatches only when a parent holds Sea Incense

Without the held item the egg gives Marill. Item: Sea Incense.