There are a number of chess openings that fall into the category of "universal systems"; sets of moves that can be played against most reasonable setups by the opponent. The Stonewall Attack, featured in the Matoewi-Phillips game
here, is one such, and another is the Hippopotamus.
The position on the left here, taken from my game against David Grant at the Wellington College International, is a typical Hippo position. It started off
1.e4 d6 2.d4 g6 3.Nc3 Bg7 4.Be3 a6 5.a4 b6 6.Qd2 Bb7 7.f3 Nd7 8.g4 h6 9.h4 h6 10.Nge2, reaching the diagram, after which I replied
10...Ne7. Those ten black moves, in some order, constitute the Hippopotamus. Note that there are some subtleties in my move-order:
a) I started off with ...d6 and ...g6 because those don't immediately commit me to a Hippo. Had white played
3.c4, I would have changed tack with
3...Nf6 4.Nc3 Bg7, transposing to a King's Indian. Only once the knight had gone to c3 did I firm up my choice of opening.
b) I played
4...a6 for similar reasons: if white does not play
5.a4, I will not immediately rush to commit my b-pawn; it may be better left on b7 or advanced straight to b5 in some lines. Once white had played
5.a4, though, I needed to play
5...b6 in order to prevent his crippling my structure with
6.a5. (Not that this is necessarily the best move, but it cuts across my plans.)
c) I made sure to play
9...h6 before
10...Ne7 because, with the white queen and bishop lined up on the diagonal, the bishop can come to h6 if I play them in the other order.
Now, you may ask, once black has those ten moves in, what does he do? Well, that depends on what white does. If white chooses to make few pawn moves himself, and develops followed by castling quickly, there is often good play to be had with ...g5 and ...Ng6 or ...b5 and ...Nb6, aimed against the king on the relevant side. Alternatively, if white has committed himself rather more, black can play for a central pawn break.
The latter was what happened in this game. It continued
11.Ng3 d5 12.Bg2 (note that white cannot close the centre with
12.e5 because it all falls apart after
12...c5 13.f4 g5!)
c5 13.f4 Nf6 14.g5 Ng4 15.Bg1 cxd4 16.Bxd4, reaching the position on the right here. I then completed my set of central breaks with
16...e5, blasting open the centre and giving me a position where I had the two bishops in exchange for white's having a central passed pawn.
Post-game analysis showed that this was not objectively justified, but the positions that resulted were extremely complex and hard to find the right moves in over the board, which is about par for the course with the Hippo. And this is the critical feature of the opening that determines whether you should play it: it's not really suitable for chasing an objective advantage that you can easily exploit, but it's highly appropriate for chasing an unclear position, one likely to be won by the player who is happier in sharp tactical melees.