Is the Hippopotamus Defense unsound?

Please bring actual facts to this discussion, such as data from computer self-play involving the Hippopotamus.  We are no longer in a world where sophistry about "opening principles" is needed.

Nonsense. One cannot play the Hippopotamus Defense from both sides any more than one can play the King's Indian Defense from both sides. If a Hippopotamus position is obtained with the white pieces, it is called the Hippopotamus Attack.

Incidentally, the Hippopotamus Attack is also a sound line of play.

@1

"Is the Hippopotamus Defense unsound?" ++ No.
Spassky played it twice in a World Championship match:
https://www.chessgames.com/perl/chessgame?gid=1106728

https://www.chessgames.com/perl/chessgame?gid=1106734

These are both facts, albeit unrelated.

@5

Those facts are related: players do not play unsound defenses in a World Championship match.
World Champions tend to refute unsound defenses in a World Championship match, especially if repeated.

Hippopotamus defense is pretty trash . It wastes its first move and white is easily winning in first move

@7

"white is easily winning"
++ Show how Petrosian could have won in the two World Champîonship games given in @4.

Sorry I think its decent I thought you are talking about kings pawn opening hippo defence

@9

"talking about kings pawn opening hippo defence"

++ What do you mean?
The second game started 1 d4 g6 2 e4, but could just as well have been 1 e4 g6 2 d4.

Petrosian blundered a pawn in game 1. Perhaps he was crumbling under the extreme psychological pressure the Hippopotamus placed on him.

If the Hippopotamus Defense is "pretty trash", as you say, perhaps you can produce a game record involving the Hippopotamus where black did not blunder, but failed to achieve a draw.

I know a guy pretty well who got to that standard playing things like 1. h4 2 h5 3. h6. An extremely talented player but an equal talent would have beaten him, more than likely.

Hi!

The Hippo is a passive defense (or even a passive "attack" when playing it as White). I would say it is the more passive variation of the Modern Defense (1...g6) as Black or the King's Fianchetto as White.

I used to play it mainly against 2200 rated engine and I know from experience you give away initiative, space, and thus counterplay. Main idea is to counterattack if the opponent overextends. On the other hand, if you start to play actively (e.g. with ...e5 pawn break) then you find yourself some tempi behind compared to the more active Modern variations where you hit the center in one step (...e5 in the active Modern vs. ...e6 &...e5 in the Hippo).

Of course your opponent should try to use all those concessions in their favor. If they feel surprised, they are the weaker player or they just not up to the challenge, then the situation changes and you can have success with the Hippo.

So is it sound? I would say it depends on your definition of "soundness". If you are happy playing passive positions, then it might be sound. In my opinion it is just about playable., not really sound. It is not a system I would recommend as main opening and not one to be played against stronger opponents.

Good luck!

Nonsense is a strong word, you clearly knew what I meant.