sound gambit against 1. d4 as black

It's impossible (playing anything reasonably sound) to reliably force the game into open or sharp territory against 1. d4. You can play 1...Nf6 and play the Budapest against 2. c4 and the c5+Qb6 line against 2. Bf4, but if they play 2. Nf3 or 2. e3 you are out of luck.

You could try for the Blumenfeld Gambit and Benko Gambit. Of course, that's not going to work against the London. I guess you could play the Old Benoni and try to get to those gambits that way.

That's a combination of the triangle slav vs. 3. Nc3 and the vienna vs. 3. Nf3.

With the triangle slav you don't actually have to enter any really theoretical slav or semi-slav positions, and in most cases you can just play these gambit lines... the most common one against the two knights setup 4. Nf3 dxc4 is called the noteboom. Against 4. e4 dxe4 this is the Marshall gambit. This one is sharp for both sides. But all these triangle gambits are sound. In the Nc3 triangle the only noteworthy line where you can't play a gambit is against 4. e3, where you can play a dutch stonewall setup or a more traditional semi-slav meran. If you're set on avoiding semi-slav territory you can go with the dutch... it's just a very specific line in the dutch, and one that's very superior since e3 has been played blocking in whites bishop, preventing some Bf4 / Bg5 lines... and you've avoided all the early attacking lines as well... objectively eval is like +0.2, alot better than the typical dutch and right on par with many other mainline positions. But I also don't think there's anything really wrong with playing a meran in this case either, it's just one part of the semi-slav, and generally that part that's considered better for black.

The triangle is fine against 3. Nf3 as well, the lines just aren't quite as sharp, and the OP was just looking for sharp lines so I recommended the vienna instead. In this version of the triangle you do still play the noteboom if 4. Nc3, which is the most common move... you can play 4... dxc4 against 4. g3 / 4 Qc2, these lines are fine, just a bit more positional than the OP wants probably. The main reason people criticize this iteration of the triangle is that after 4. e3 Nf6, trying to enter the semi-slav, white can delay Nc3 and there are some b3 / Nbd2 setup that are stronger than your typical semi-slav... this bothers some people... but it's objectively fine, like +0.2. But you can also just play your dutch setup again here if you want and it's just as good as in the other triangle.

If I were playing one triangle I'd just play both triangles. However, for the OPs purpose where he's looking for sharp lines the Vienna does well since it's probably one of the sharpest lines against 1. d4... we're fine playing this instead of the triangle because we're avoiding mainline semi-slav positions in the other triangle anyway, and a repertoire based on gambits is already going to be very compact to where you're not really worried about maximizing redundancy. After 3... Nf6 the only real serious moves white has are 4. g3 (the catalan) and 4. Nc3. The other moves are generally considered crap. Hence... you need something against the catalan, but other than that you can just play the vienna.

There are other interesting options besides the Vienna too, though - you can also go into the semi-tarrasch (which can be sharp if you want it to be). In general I don't see much problem with mixing and matching openings like this if you're playing the sharp gambit lines.

I looked at your ratings in your profile, you are at the stage where more serious opening preparation is needed, with your opponents starting to know how to correctly reply to various opening schemes that are popular at lower ratings.

But but but I like gambits

I think I’m going to try the stonewall Dutch for d4. It gets some play at the GM level so maybe it will be good for me for awhile. I doubt many 1700-2000 know it well. I pretty much just play the Indian game now, what I’m doing is working for my rating but I’m kind of just sick of those positions at the moment.

I’m going to look into the stonewall Dutch and watch a few videos then try it out. It seems interesting and I’m guessing it’s pretty uncommon. I really don’t like the idea of having my king cracked open but I’ll give it a whirl.

A gambit in the Nimzo Indian. But I'm not sure how (un-)sound it is.

Well this is just a very specific line in the stonewall dutch. If you want to play the entire stonewall dutch... that's alot more risky. Especially the 1... f5 move order. Still might be fun though. You can also reach it from 1... e6, there are still some early move order issues but it's not too bad. Main issue there is you'll need to play the french.

However, in the mainline stonewall dutch usually white starts with g3 and doesn't touch the e pawn... Bf4 here remains a strong option (which challenges blacks bishop, exacerbating blacks darksquare weaknesses), and there are also some early issues with Bg5 move orders, etc. In the triangle move order Bf4 isn't possible, and it bypasses all the early move order issues. Also... f3 > e4 is another common plan but it's down a tempo with e3 being played.

Furthermore, in the Nc3 triangle it's even better for black because Nc3 is generally considered a mistake, it's hard to reroute the knight to an active square from there, it also blocks Bb2, and Ba3 is also not possible.

But the mainline stonewall is still playable, just some difficulties involved. 

In the stonewall main strategic issues are the darksquare weaknesses in general, and developing the lightsquare bishop. But it's a solid position objectively speaking. Which is not something you can usually say about the dutch. Your king is actually more safe than in other dutch positions due to c6 bolstering d5, the diagonal usually won't open up until you're ready for it

Here's a nice video - The Stonewall Dutch · Chess Openings - YouTube

sound is a not a proper noun it's a common noun.

haha just a gambit that isn't trash if the gambit fails. From what I am gathering there really arent any against d4 which annoys me. I'm learning and playing the dutch now and am not a huge fan but its nice to mix it up from indian games , slavs and london systems.

You could go with a Blumenfeld and Nimzo-Dutch repertoire for very aggressive yet still relatively sound gameplay which will usually lay outside of your opponents' theory books.

On chess.com, maybe 1600s may not know a lot of openings well. The knowledge curve starts going up severely after 1600. For in-person over the board ratings...you will run into significant opening preparation around 1400. Someone mentioned the Albin Countergambit...a friend of mine who plays it unpleasantly discovered all the 1300s - 1400s knew the exact and correct responses during an in-person rapid chess tournament.

Not my experience tbh … I beat a NM last week with the smith morra gambit. Not worried about 1300s on here or uscf …. When I play open on the low end I’m something like 90% against them. My last 3 games: wins vs a 2286(French), 2086 (giuco), 1707(Dutch). I’m pretty underrated because I play tons and tons of unrated on here and ranked on lichess. I play solid stuff generally, a few gambits like the smith morra and scotch. But I have over 1100 games in the caro kann and I have pretty much every variation down as black at this point just from playing and analyzing. I just play and analyze right now and it’s working really well. I’ll be 2000 rapid and blitz mid 2025 I guarantee it… I went from 1600-1700 blitz in 1 day last week and went back to unrated playing up.

haven’t studied any openings aside from watching 20 minute Igor Smirnov opening trap videos. I rarely lose in the opening, usually it’s due to just playing too fast which can be a blessing and a curse.

purpose of this post was just some ideas for some weird stuff against d4 and I landed on the Dutch which I’m finding out I actually need to study extensively to be effective… but since it’s offbeat I think it might be worth doing.

Not trying to be cocky or a jerk at all just saying what’s working for me… I will keep doing this till it stops working.

Dutch 1...f5 is fine against 1.d4. You will hear people say it is not sound, but that is rubbish - at least below GN level. I play it with fine results.

Benkö 1...Nf6 2.c4 c5 3.d5 b5 is a sound gambit, but 2.Bf3/2.Nf3 won't allow that.