Here's another thought about the Cube being the artifact that changes Algrim: maybe it's Algrim who changes *himself* with the Cube.
It's a fairly mundane solution, but one that's a lot cheaper for the studio bean-counters: instead of introducing (and casting) a whole 'nother character with godlike powers to create Kurse, and instead of letting the Cube fall into enemy hands yet again, why not just have Algrim try to take the Cube from Odin, and accidentally/intentionally wind up getting morphed into Super Darkelf?
There's that report of AAA having a scene with Odin and Frigga, and Frigga (allegedly) dying at some point; so maybe Algrim makes it to the Asgardian throne room, confronts Odin and kills Frigga and/or The Allfather, and takes the Cube (either for himself, or at the behest of Malekith, or even Thanos if he shows up after all). But the power is too great for him, and he winds up becoming a twisted Hulk-like monster.
THE COTTON AVENGERS
...They move like slick cotton on oil.