The rules are in German.

English rules: chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/https://fgbradleys.com/wp-content/uploads/Skull-King-Rulebook.pdf?srsltid=AfmBOoowdWx7p6J2pC_oPOJJ891-4QTZ9dez8vA7bEo3iA2cG0zzdI2j

Skull King is a trick-taking game similar to 'Oh Hell!', 'Wizard', 'Eucher' and 'Spades', with players needing to state how many tricks they think they'll win each round. A unique element of this game is that bidding takes place simultaneously, leading to rounds that are sometimes over, or under-bid. As players must win the exact number of tricks that they bid to earn points, winning too many tricks is just as bad as winning too few and this leads to intense competition where losing a trick can be as exciting as winning one.