It is unlikely that it be:
Klunk - He's a vacuum cleaner…
It could be:
Vorselon - He did get squished and turned into a ton of bolts, but remember Klunk? Plus it seems like there has been enough time for him to get back on his feet.
Klunk - Again, the thing with Klunk was non-canon, but he could still be as dead from the battle on Metropolis, or he could've been canonically repaired and become a villain? Even if SAC was canon, don't forget his eyes glowed "ominously" at the end, so he could still return? A villain who is in the form of a vacuum cleaner might be quite funny…
Vorselon - Given that Vorselon's death only happened in that weird timey-wimey-wibbly-wobbly space between the end of the game and challenge mode, I'm also not convinced his death was canon either, but I'm really not sure…
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