If they can show that the tracking was without a doubt taken from the original videos then I think they have a case. Since EPIC is making money off the dances these lawsuits are worthwhile for them to pursue. If the dances were just free (like homage dances in other games) I doubt EPIC would be facing legal action like this.

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Alfonso almost definitely has a case since it's very clear that the tracking was taken from his Dancing with the Stars performance. I don't know if they used any tracking on 2 milly but the Floss Dance was possibly tracked from Backpack Kid and he potentially has a case if Alfonso does. Orange Shirt Kid has no case, they clearly had at least a competent adult recreate it for the tracking in the in game version of the dance and it's not an original dance.