A hippogriff is a legendary creature, supposedly the offspring of a griffin and a mare. Anybody who’s seen a Harry Potter film could probably tell you what one looks like.
In the world of playing cards, a hippogriff is a mythical suit chiefly used in an anecdote about a man who dreamed he held the perfect notrump hand with 13 sure winners against a stranger (Satan), who was on lead. Satan proceeded to run 13 tricks against the man by cashing all the cards of a weird greenish suit called hippogriffs.