and how do you get mamu ;-;
The hints to get Mamu are: Its something in the village, it requires a specific building at level 3, its sorta related to cold, its something you wouldnt normally do. You will know you did it right by the team select screen.
If you want the exact solution
SPOILERS BELOW
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Build a Level 3 Nest, but do not put any monsters on it, then begin a run and mamu should be selectable.