Consider increasing Libido crystals reward during event (currently 5 as as reward for last extra goal in Colosseum event), as the number of Mythic girls with ability upgrade has been increased - just 5 crystals alone during one week doesn't make up for it (yes you can get them as top daily ranking rewards - But there is too much tussle for top spots). You can do this either by directly increasing reward to 10 or increase the extra goal for Colosseum event.