It has been tried after 1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. g3 (4... Nxe4 5. Nxe4 d5 6. Nc3 d4), even by decent players. But that's only because 4. g3 is a bit slow. Against more energetic moves Black has no shot at this.
Can Halloween Gambit be played using black?

That's not because g3 is slow.
Halloween gambit against 4 knights g3 (Glek system) is an improved Halloween because g3 prevents the reply Ng3 and weakens white's kingside.
But sure, white can decline it and going into a main line in this system, like this :
I think that's all about playing Halloween gambit as black.
Can Halloweem Gambit be played using black?
Any tutorial regarding this?