Annotated chess game

King's Indian Attack (?). Pirc Reversed.

A tad conservative considering the position is colours reversed and hence giving White a 'defence' with a move in hand. One might have anticipated an Austrian Attack, here. But the situation probably calls for a more subtle approach than the usual methods White takes against the Pirc.

I agree that something like f5 is definitely an interesting option, leading to a sharp position with colors reversed. This idea of f6 is similar to what white sometimes plays in some Sicilian lines with f3 to stop a Ng4, and then castling queenside. I might have considered a Be7 instead of f6, stopping the same threat but leaving kingside castling as an option as well as Nf6 instead, for a more solid set up.

If he didn't want to exchange Queens after 5.e4(?!), then maybe 5.Nbd2 was called for. Another move I used to like in this sort of position was c2-c3 (actually ...c7-c6, colours being reversed) with the idea of placing the Queen on c2 (...c7) , and then following - at a suitable moment - e2-e4 (...e7-e5).

This move doesn't show up on the databases I have access to. The position doesn't show up at all, which really shows how dubious it really is. If I were forced to play this with white I'd either go for O-O or c3. Nbd2 seems ok but even just the normal Be6 after and it seems like black is already better.

I believe this kind of thing is called the 'Hippopotamus'.

Well a true hippo would have a pawn on e3 and his Nf3 on e2 instead. en.wikipedia.org

This idea has basically been forced since you played f6, and is kind of the reason I prefer Be7 - your king side, while getting ready for a pawn storm, is still underdeveloped and white isn't actually forced to castle kingside.

I don't reckon castling long was going to feature in White's immediate plans.

White might well be planning c2-c4 soon, which would transform the thing into a Closed Double-Overhead Reversed Twin-Cam Sicilian.

In principle, flank attacks are more likely to succeed if the centre is closed. For that reason 10...d4 was well worth thinking about. Having said that, I don't reckon White's counter-chances on the Q-side subsequently are too bad at all after 10...d4, 11.a3 with 12.b4 to follow.

I wouldn't mind knowing why you think this is a mistake. I agree it is slightly premature and gives white counterchances they might not have with 10..d4, or similar but you still look better to me. Your king is safer, your pieces on good squares and even if everything gets traded on d5 endgames favor you based on your extra space.