A graph showing how many rolls you'd need to get the ships on the upcoming event : r/AzureLane
WoWs Gamer Blog
Azur Lane Dreamwaker's Butterfly Event - Gachazone
Azur Lane - Office of Naval Intelligence - Notable drops for Worlds 1 through 3. Please keep an eye for them while playing! Biggur: https://imgur.com/I7rjw6G | Facebook