@1
"What are the general differences between a Hipopotamus defense and a Hedgehog defense?"
++ In the Hippopotamus black fianchettos both bishops and places knights on d7 and e7 and refrains from c5 or f5 until white moves.
https://en.wikipedia.org/wiki/Hippopotamus_Defence
In the Hedgehog black plays c5 and knights go to f6 and d7 and at first only the queen's bishop is fianchettoed. The king's bishop first goes to e7, but is later re-routed by Re8, Bf8, g6, Bg7.
https://en.wikipedia.org/wiki/Hedgehog_(chess)
First time playing against the Hippopotamus Defense. Game in 15 aka a Rapid