1-2. school daze
3. the maud couple
4. fake it 'til you make it
5. grannies gone wild
6. surf and/or turf
7. horse play
8. the parent map
9. non-compete clause
10. the break up breakdown
11. molt down
12. marks for effort
13.
the mean 614. a matter of principals
15. the hearth's warming club
16. friendship university
17. the end in friend
18. yakity-sax
19. on the road to friendship
20. the washouts (episode)
21. a rockhoof and a hard place
Well, when you explain it like that: An entirely reasonable motif, despite not matching what the show animators decided fitted their audience, medium, and/or budget best!
Edited
In my head, Nightmare is more or less the opposite of Luna. A dark starless night filled with monsters and dangers. I wont claim that her mane being starless was intentional, but I found it quite fitting and with her smoke trying to blend the stars out fits even more into it. Also, the picture would be quite “overloaded” with her having stars in her mane too.
Edited because: Spelling
Not much stars in her actual mane and tail here… more like they fail to obscure all the stars in the night sky behind her than and there is a separate smoke/flame effect her presence is causing to rise the ground rather than, “my hair is the Milky Way that moves like flames under my command” (which is how I would describe her appearance in Ponyville Town Hall).
Edited