3.c4 e6 is the Icelandic Gambit, while the Portuguese arises after 3.d4 Bg4. At the GM level, 3.d4 is much more common than 3.c4.
Gambit against 1.e4?
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If you are planning to play the Portuguese or the Icelandic, White might be a spoil sport (me) and after 1.e4 d5 2.ed Nf6, play 3.Bb5+ Bd7 4.Be2 Nxd5 5.d4, when the play resemble the 2...Nf6 Scandinavian main line (1.e4 d5 2.ed Nf6 3.d4 Nxd5)
Though engine refuted (+.9 or something), the Rousseau gambit has been great to me from 600-950. It's like a reverse vienna off of the Italian game. Black is better if the pawn is taken, and it is extremely easy to neutralize. 4. d3 is a the best move for white, not taking.
The Two Knights Defence:
1 e4 e5 2 Nf3 Nc6 3 Bc4 Nf6 4 Ng5 wins a pawn by force for white
The Marshall Attack:
1 e4 e5 2 Nf3 Nc6 3 Bb5 a6 4 Ba4 Nf6 5 O-O Be7 6 Re1 b5 7 Bb3 O-O 8 c3 d5
I believe the Portuguese is 3...Bg4 vs. 3...e6 for the Icelandic Gambit, right?