The Metal Hippo is a stronger version of the regular Hippoe. Its attack rate is faster, and it has more health, along with an ability that only metal enemies have: taking 1 damage per hit. It has 80 health in total, with 2 knockbacks.
In some levels, Metal Hippoe can act as an annoying meatshield, such as in Chubby. B. Goode and Prison Destruction, and other times it can be a help for stalling as you build up long range cats.
Dictionary
English Version
A certain organization decided to experiment and make Hippoe's body metal. Appears to be weak to critical attacks.
Japanese Version
Encyclopedia entry.
Rough Translation
連邦政府の改造手術により生まれ変わった
ハガネの肉体を持った改造カバ。
クリティカルな攻撃が弱点らしい。
It was reborn by remodeling surgery of the federal government Remodeling hippopotamus with a body of steel. Critical attack seems weakness.
Strategies
If the player doesn't have Fish Cat at its true form, the player can still use Jurassic Cat, Rope Jump Cat (from defeating White Cyclone Stage), Space Cat (from defeating Red Cyclone Stage), Crazed Fish Cat, or Marauder Cat to deal criticals. Player can also use fast attacking cats or long range cats to build up damage, such as Cow Cat or Gross Cat.
For status effects, the player can use Bronze Cat (from defeating Black Cyclone Stage) to knock back or Hoop cat (from defeating Metal Cyclone Stage) to stop Metal Hippoe.