Hippo Defense is nothing but a variation of Modern Defense and its indeed a very exciting opening. I started playing chess since last 4 months and was struggling to find a pet opening which I could play comfortably with and arrive at positions which I was familiar with.Then I came across Nigel Davies's games online and saw this fascinating game of his in which he played modern defense in hippo style and thrashed his opponent. I started seriously learning this and then applied it in blitz games with pretty devastating effect as black. I am still learning the intricacies of this opening which is so very flexible that once you understand the underlying idea behind it,you can play real decent games without getting whopped. Again,remember you need to be patient when playing with this,slowly cutting off good squares for his/her pieces,gaining spatial advantage mostly on Q-side and punching holes in his center.From my experience,I have seen many opponents in bltiz,trying to attack from all sides and once you fend them off,their pieces end up in wrong positions and then you get to him them.Basically,you got to be lurking under the water level and then pounce on your opponent quickly.Like shock and awe tactics.Having said that,if you play too passively,you are going to be steam rolled by white's center and then your K-side.Every day I discover something new about this opening.My personal advise is,keep testing it in your blitz games,fine tune it,rinse and repeat until you get a hang of it and can come up with a skeletal plan for your games.Initially you are gonna lose,but then again you learn more when you lose and then win.
Below is a blitz game which I played yesterday.Hope you find it informative.Hit me up if you want to practise this along with me.Would like to learn new ideas from others too.
The hippopotamus is usually followed by either a crushing defeat (serves you right for insulting them repeatedly) or a psychological breakdown from the other side, resulting in terrible moves to try to break through the pawn line, which becomes a mistake, leading to more and more mistakes and eventually a very one-sided checkmate.