Scryfall Card objects now include new preview[previewed_at], preview[source], and preview[source_uri] fields, which contains information about who previewed/spoiled this card, updated as soon as we enter the card during a preview season.
Deprecation Notice: Frame Effect Field
On Oct 1, 2019, Scryfall will be removing the frame_effect field from Card objects, use the new frame_effects field (plural), which can contain multiple values.