Being slow doesn’t mean it’s bad. Anyway, Hatterene has amazing special attack and great defenses. I’d say Hatterene is a very good Pokémon. Yes, speed is important, but speed isn’t everything, and when you look at Hatterene, it doesn’t need speed. Here’s a set:
Hatterene @ Life Orb
EVs: 252 SpAtk, 252 HP, 4 SpDef
Nature: Quiet (+SpAtk, -Spe)
Ability: Magic Bounce
Trick Room (Low speed pays off)
Hatterene is a very nice Pokémon that I recommend using. Hope this helps!!!