Crystals on Laputa

Gaining crystals currently in Laputa to unlock 8th slot is extremely hard as the crystals rarely appear on the spinner and even then you gotta hope the spinner lands on them. I suggest a better way would be for crystals to appear every time on the spinner and even better have half the spinner containing crystals because at the rate I'm going atm I'll have died of old age before unlocking the 8th slot!