It's an artificial Zoan type fruit

I already know that but why is Hiyori telling Zoro it's the fault of SMILE everyone's laughing at Tonoyasu's death.

because they can't display any other emotion but joy, their smile is essentially a permanent mask that can't be taken off no matter how the person is truly feeling

since they didnt get powers, they only get the downsides of the fruit.

Thank you! I was really curious about this.

Yeah and they also can't swim