This means "great disguise", and the specific person that was being referred to by this phrase was wearing a costume.
Why do i need the le is it because of specificity or it is an idiom?
On utilise "le" dans ce cas seulement:
Exemple:
Mais par contre / sinon on dirait:
Super le déguisement doesn't exactly mean "great disguise".
It would be better to write it with a comma and an exclamation mark:
Super, le déguisement !
That means:
(Il est) super, le déguisement ! (It is) great, the disguise!
Il me semble ici que 'le' sert à mettre l'accent sur l'objet de la réaction produite, le déguisement. 'Super déguisement' se dit aussi, mais me semble comporter un 'degré' d'emphase moindre.
e.g. in english :