all the number cards in yugioh zexal Complete Custom Deck for Yu-Gi-Oh! Yu-Gi-Oh! Wiki - Number S0:

I kind of hoped this would find its way into Standard when The Brothers War (BRO) released, given its relevance in regards to that set, but alas

The sun and moon combine in this card, with the former shining through on the bottom while the latter glows on the upper right

It has an interesting restriction on when it can be cast for free, but not nearly prohibitive enough to make this card bad

I Am Duskmourn Ongoing Scheme (An ongoing scheme remains face up until it's abandoned.) At the beginning of your end step, you may cast a spell from your hand without paying its mana cost

Actual sale history isnt widely available, so you can only guess why the market is treating this trainer with such hesitation

Nintendo World Report