4 days in a week you shall have dayly missions for dragons (for example tuesday - blue, monday - red etc). Only t3 missions does matter - chance to get 100 lvl dragon on t2 mission is too low, so do t1 and t2 only to get FG.
And when you could farm those 3 100 lvl dragons for upgrade 5* girl - you should have dozens of 20 lvl ones, so as i said they're a garbage, and 6* girl requires all 5 100 lvl dragons and it becomes a pain besides events.
And 5lvl dragons are garbage from garbage because u need them only for 2* or 3* girls wich you want evolve only if you like their appearance - they're too weak. I have maxed Nymphea, so i know what I'm telling.
BTW, i forgot to say that you can use only 100 ampies of each type per girl(3k hp, 1k attk, 400 def)