Erfworld, The Thread.

[Calemyr]

Maybe, but that would mean that dittomancer would be doing a much better job of croakamancy than a croakamancer, since people can be presumably duplicated again, and dittomancy doesn't require the original to be croaked.

Not exactly - dittomancy could work that way paired with predictomancy (is that the right name?), but otherwise it's kinda the opposite of croakamancy. The target has to be alive, which means you can only use it before you know you need it, and the clone seems to be of the same nature as the original so it can't be used to subvert enemy forces.

We also don't have many benchmarks for the duration of duplicates - while mass uncroaked units are listed as lasting a few turns, a mass duplication apparently lasts a mere attack action; a focused uncroaked unit can last a decidedly long time (judging from the initial GK warlords), which would logically make a focused duplicate last a few turns.

Other than that, it's got a large number of applications, primarily as a force multiplier rather than merely adding another unit. Limited juice means that, under most circumstances, it isn't practical to use it this way.