From the Super Mario Wiki, the Mario encyclopedia
Unlike with Harimen, performing a standard Smash Attack around a Harimen Zetto will not flip it over, instead causing it to walk towards Wario. To flip a Harimen Zetto, Wario must either perform a super ground pound nearby, throw a rock or a regular enemy at it, or hit its underside with his head from below. Enemies thrown at a Harimen Zetto are defeated, and heavy enemies such as Ringosukī can be used to defeat a Harimen Zetto instantly. They can also be defeated instantly by Fat, Frozen, or Zombie Wario, or by rolling into them. When defeated, they yield three silver Coins. Wario loses a gold Coin (or equivalent if he does not have at least 500 points) if he is hit by them.
Harimen Zetto are fairly rare to encounter. On Super Hard mode, most Spikys are be replaced by Harimen Zetto.
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