An invisible ink card is a special variant of the regular version, that basically looks the same, but is exclusively foil and has extra in-universe text from the investigative crew taking notes about the character
UR Ultra Rare Dark Ruler No More X SPELL Negate the effects of face-up monsters your opponent currently controls, until the end of this turn, also for the rest of this turn after this card resolves, your opponent takes no damage
1 Traditional foil rare or mythic rare card Here, you get a single traditional foil rare (76.9%) or mythic rare (12.8%), or 1 of the 7 lurking evil rares (9.0%) or 2 mythic rares (1.3%)
VSTAR Powers are limited to once per game, making them the ultimate reset button for a match
Mari, the Killing Quill: This is an interesting one
However, the flip mechanic did give players one of the best holiday-inspired cards ever printed