Quote Originally Posted by Talith View Post
Puzzles and Dragons. They have a way of converting premium rolls into Monster Points you can then spend on OP cards as well as some token waifu cards. The prices are mostly aimed at whales though.
That sounds about like Rainbow Crystals. You get them from discharging non-fodder units of gold+ rarity, with the amount gained being as follow:
Gold: 20 (non-event), 1 (event)
Platinum: 100 (non-event), 3 (event)
Sapphire: 1
Black: 400 (non-event), 15 (event)

So far there have only been 3 units to spend them on. Two blacks, each costing 1000 rainbow crystals, and one platinum costing 400 rainbow crystals.