If you loved Batman Unlimited: Mechs vs. Mutants, try Justice League: Throne of Atlantis
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Batman Unlimited: Mechs vs. Mutants
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Justice League: Throne of Atlantis
What they share
Theysit in Action / Animation / Science Fiction territory. If that's the register that drew you to Batman Unlimited: Mechs vs. Mutants, the second film will land in a comparable space — through a different lens.
What Justice League: Throne of Atlantis is
You live with unexplained powers in a world on the brink and then underwater kingdoms declare war on the surface, the Justice League forms an alliance with a young hero, Ethan Spaulding brings this aquatic battle to life.