Налажал ты с отступами, анон. Я пофиксил:

def possibilities():
    alphabets=(n,o,r,t,h,e,a,s,u,w,m,y)
    combinations=list()
    for n in range(9,-1,-1):
        for o in range(9,-1,-1):
            for r in range(9,-1,-1):
                for t in range(9,-1,-1):
                    for h in range(9,-1,-1):
                        for e in range(9,-1,-1):
                            for a in range(9,-1,-1):
                                for s in range(9,-1,-1):
                                    for u in range(9,-1,-1):
                                        for w in range(9,-1,-1):
                                            for m in range(9,-1,-1):
                                                for y in range(9,-1,-1):
                                                    if len(set([n,o,r,t,h,e,a,s,u,w,m,y]))==12:
                                                        north=10000*n + 1000*o +100*r +10*t +h
                                                        east=1000*e +100*a +10*s +t
                                                        south=10000*s + 1000*o +100*u +10*t +h
                                                        west=1000*w + 100*e +10*s +t
                                                        earth= 10000*e + 1000*a + 100*r +10*t +h
                                                        if north +east +south +west == earth:
                                                            combinations.append((north,east,south,west,earth))
                                                            return combinations

Вот теперь всё работает!