Thor's mystical hammer Mjolnir is his most trusted weapon. The God of Thunder is able to wield it since he's deemed worthy of doing so. Appropriately, an evil version of Thor had his own version of Mjolnir - and was able to use it since he was unworthy.
Mjolnir (as well as Thor) first appeared in Journey Into Mystery #83. The hammer is made from the Asgardian metal Uru and is enchanted so no one can lift it unless they are worthy. Heroes who have wielded Mjolnir include Thor, Beta Ray Bill, Captain America, and Jane Foster. The powerful weapon also has evil alternate versions, including one that was fit for those who were unworthy.
In Avengers (2014) by Jonathan Hickman and Esad Ribic, the supervillain organization A.I.M. (Advanced Idea Mechanics) brought a group of evil Avengers who's Earth just crumbled into the main Avengers timeline. Among them is Thorr - who immediately demands respect on his new Earth when he first interacts with people. When he sees that people aren't kneeling to him, the evil Thor decides to strike the ground with Mjolnir and kill the innocent bystanders.
When the Avengers finally meet up with their evil doppelgangers, they engage in a wild fight. Iron Man battles a version of himself where Jarvis is inside the suit. Captain America takes on a somewhat similar version of himself. Meanwhile, Thor takes on the killer Thorr. However, Thorr offers Thor a deal to join him so that they can rule the world together as Gods - Thor doesn't agree to the arrangement. However, Thorr loses his hammer when the Avengers execute a sneak attack which sends Mjolnir to the ground. The inscription on Thorr's hammer reads "whoever holds this hammer, if he be unworthy, shall possess the power of Thorr." The words are exactly the same on the original Thor's hammer, except to wield the evil version, you must be unworthy.
The fight is put to an end once A.I.M. soldiers use a temporal shield to displace the two warring Avengers teams in time. In a surprising act of kindness, A.I.M. offers the evil Avengers a new Earth to return to since there's was destroyed. The evil Avengers depart to Earth-83-292, a world where there are no Avengers and the group can exist and act without doppelgangers. While Thorr didn't stick around for long, the fact a version exists where being unworthy is necessary in order to assume the role is appropriate. Even evil Thor needs to fit the part.