what do you mean by “I exported my re-targeted character to another”? I’m not sure you can export outside UE4 the retargeted FBX skeleton, as the retargeting options that the plugin modifies are UE4 specifics (i.e. the underlying skeleton is not modified). In general, after you have applied the plugin on a Mixamo model, if you have an existing UE4 animation then you can retarget it (the UE4 animation) to the modified Mixamo model. The retargeting is then computed by the UE4 editor using the informations computed by the plugin. You can see it at time 2:50 in this video: ?t=2m50s (I suggest to look at all the video).