So I got to chapter 21 and a thought occurred to me, "Can I just do this quickly with Corrin and Camilla only?" This is on hard mode:
[spoiler=Corrin]
Paladin lv.8: hp38/spd29+1(GY)/lck20/def20+1(GY)
[spoiler=Camilla]
Wyvern Lord lv.12: hp32/spd25/lck16/def26
C-support
Spd/def +1 from meal, Camilla boosted hp/spd/lck/def from tonics
Camilla had an iron axe, vulnerary, concoction, and elixir
[spoiler=turn by turn]
1: Corrin and Camilla next to each other, Corrin dodges rock
2: Corrin pairs up with Camilla, dragon vein
3. vulnerary, had to dodge at least 1 rock, leveled str/skl/spd/lck/def
4. elixir
5. win