I completed the single rare recipe mission and it reported that it returned nothing, likely because i had all the recipes of that rarity. I checked, and (surprisingly) i had all the rare recipes EXCEPT for Biff the Rabit. He has no recipes, but his gear is rare or better.
Event Crusaders have their recipes locked for the entirety of the event and for the 2 weeks after it ends. Biff's recipes will be available to obtain starting Apr 17th at Noon Pacific Time.
 "Crusaders of the Lost Idols"){kind=icon}
 "Idle Sword 2"){kind=icon}
 "The Perfect Tower"){kind=icon}
 "Bloons Monkey City"){kind=icon}
 "Valthirian Arc 2"){kind=icon}
Event Crusaders have their recipes locked for the entirety of the event and for the 2 weeks after it ends. Biff's recipes will be available to obtain starting Apr 17th at Noon Pacific Time.