Never Encountered Anything Like this Before (I play black)

Note: I went over this game with the help of an engine. The move 8 alternative line is not my creation.

As the immortal Wang Chung said, "I'd either swim or I'd drown.  Or just keep falling down and down."  The advance variation often leads to positions like this, where white advances his pawns like crazy, and stands on the knife's edge between having a huge space advantage and black tied up, and positional collapse.  These positions tend to be frustrating either way -- i.e. white can simply be winning, and then make one wrong move and the position collapses.  Or black is constantly looking, and never finds the flaw that turn's white's position into swiss cheese.

I believe 4. ... h5 is a bit more commonly seen, although 4. ... h6 is not bad if played properly.  

I guess I should've learned more opening theory.

i think your oppoment was a sandbagger

looks quasi-engine'ish to me...depending on how much time btwn moves.

It's actually blacks 6th move - Bh7 that is a known inferior move in this position. You should have played Bd7 instead. 

My personal experience (with the white side) after Bh7 is about a 70% kill rate. 

That's what I thought at first. But the first 9 moves were actually book and have all been played by masters.

yes, 7. e6 ! is usually crushing sadly.

A fun game to play through.  Comments in the notes.

I'm glad someone's having fun.

Qg3+ was an "in between" move attempt to force white to forfeit castling rights. I technically got what I wanted but I didn't account for white simply castling by hand.

Thanks for the analysis.

Yeah, I suspected that was possible. As I said, they only made 1 "inaccuracy" and had an average centipawn loss of 16 (which is insanely good!). All of their opening moves were played quickly.

I figured they just had that book line memorized, but that seems like a highly esoteric thing to spend time on. I wouldn't expect anyone short of an IM to have exact knowledge of that rare line. They may have been using an opening explorer which is forbidden by the site this was played on.

There is a book called: "My first chess opening repertoire, for white" by Vicent Moret, that teaches precisely this line of Caro Kann for white. So I'd guess your opponent got this opening memorized from this book. I'll check his games if he plays the book recommendation against other openings.

Maxime Vachier-Lagrave, also played this line a couple of times. It's not all that unknown.

In Chessable there is a book called "The cavemann Karo Kann" where it teaches this variation for white.