What Openings do you consider very tricky or complex?

i would respond 2.d4 after 1...Nc6 though

Agree with CS007

Well that is the mainline Chess and Christian, but it doesn't mean Nf3 is never played. If Nf3 is played, you can easily fall into a ruy, italian, scotch, ponziani, etc. That is why Nf3 f5 could be very tricky. 

ok well the main reply is d4 which i think is a good reason it wont be played much

well, d4 is solid, but it leads into the nimzoswitsch defense, which is an uncommon line that many players get into trouble with. Ask NM aww-rats. He can tell you all about it :)

i like white better in the nimzowitsch. Also I thought that 1...Nc6 was the nimzowitch (keep getting tempted to shorten it to the nimzo - but thats in nimzo indian!)

the main line of the Nimzoswitsch is 1. e4 Nc6 2. d4 d5 and then white can play lots of moves, but has to know theory. 

ok thanks pawnpusher

I would think that the KG, EG, and maybe The Halloween Gambit are tricky

here is the last one

That line is actually not the mainline. In fact, that line is a bad line for black. There are many other opportunities for black to do better in the position. Giving back the knight is always an option as well, and if black gives back the knight, he will almost always end up in a better position. This is a good line:

you can always play the Ng6 line as well and easily secure an advantage. 

yeah, but for someone who doesn't know how to handle it. it can be deadly. heck even if they know it it can cause them to think.

but it is not the best opening available. I just hate the 4 knights.

Najdorf - Poisoned Pawn 

The Najdorf PP, Samisch KID, Botvinnik Semi-Slav, King's Gambit, Dragon Sicilian, etc.

I don't know about tricky, but I have agrresive lines 

Blackmar-Diemer Gambit Accepted can be tricky at an amateur level.  I've been beaten by it and won more than a few with it.

The halloween gambit is unsound because of the Ng6 lines and lines where black gives back the piece. However, I believe the following gambit is considered sound:

I don't like facing the Ng6 lines, but I would not call it unsound.  It is just not as good as the Nc6 lines.  And giving back the knight, that doesn't help Black at all - that plays into White's hands.