Add to pony.ini of Nightmare Moon:

Behavior,"NMM Luna",0,5,5,0,"stand_right.gif","stand_left.gif",None,"NMM Luna 1","","Luna",True,0,0,"Princess Luna (Season 2)"
Behavior,"NMM Luna 1",0,4,4,0,"stand_right.gif","stand_left.gif",None,"","","Luna 1",True,0,0,"Princess Luna (Season 2)"

Speak,"Luna","But... what about our eternal night?","",True
Speak,"Luna 1","???","",True



Add to interactions.ini:

NMM Luna,"Princess Luna (Season 2)",0.2,200,{"Nightmare Moon"},False,{"NMM Luna"},300