Every Gigantamax forms has additional effect to their type.
But I don't know what Hatterene has. Can someone tell me?
I'm going to assume that you're talking about G-Max Smite, which is Gigantamax Hatterene's exclusive move.
The effect of G-Max Smite is that it confuses all opponents.
Source: I have G-Max Hatterene and I've used G-Max Smite