Had this on hand for a while, but I don’t anticipate making any further changes, so:
This patch adds stat bonuses to recruitable enemies, and Roshea, based approximately on the bonuses generic enemies receive in Maniac mode; these bonuses were manually entered into character data and so will not scale down or up with the selected difficulty.
Download the patch here.
View the changelog here.
Naturally, some enemy-joiners who were already good (eg, Darros, Etzel and Sirius) become unreasonably strong under these conditions. If that bothers you, or you want non-enemy joiners to be improved as well, I’ve set up an alternate patch (link) which buffs a wider array of units. You can find the changelog for the alternate patch here.
Both patches are to be applied to a translated FE12 ROM file.