theyre secrets, theres been some hints around related to them

Mamu:  Requires a specific tier 3 building in the village, something you wouldnt normally do, tangentially related to cold.  

Nessa: Requires a specific Egg, Related to Birds, related to warmth.  Cannot be done in Zone 1 but does not require infinite mode. 

I will admit they were rushed secrets so theyre abit more obtuse than Tama.  Let me know if you want the exact solutions