2 Lokis, both with not the best ivs

+Res, -Atk;
Although -Atk hurts her healing and combat potential, she still keeps her base 35 Spd to survive against mages. Not only that, but Res is a superboon for her which helps her even more. Even with +Def, she's still likely to be KO'd by physical units; even moreso with -Spd.

Keep the +res-atk and fodder the other for C duel skill.

I see people recommending foddering C duel. Everyone agrees that this skill is functionally dead on most units (Loki being a notable exception) and that it's a scoring mechanism.

I'm making the case that if you're thinking about foddering it, better to wait for a few updates, see if arena crowns mean anything. If not, you would probably do better to fodder atk wave or the balm.

https://fireemblem.gamepress.gg/q-a/those-thinking-foddering-c-infantry-duel