Apparently it having “Over Valhalla” was intentional, as cosmic horrors and eldritch summoners are also included in the pack.

You know their names, but you dare not speak them! Drawn to the light of a trapezohedron, three new ancient Entities emerge from the depths of eternity to exert their maddening influence over your Duels. But those aren’t the only strange happenings afoot… Aleister the Invoker resumes his experiments, but gets a little more than he bargained for in Shadows in Valhalla! In addition to tournament mainstays like Aleister the Invoker, Invocation, and Invoked Mechaba, this booster set introduces a Link Monster version of Aleister that gives Duelists greater access to powerful Spell and Trap cards like Invocation, The Book of the Law, and Omega Summon.