Hatterene is fascinating from the standpoint of a Magic Bounce user. Unlike Espeon, Xatu and Mega Absol who are frail (and Mega Diancie/Mega Sableye which ate up your Mega Slot), Hatterene is bulky, enabling it to come in repeatedly on Entry Hazard setters and giving you room to breathe if you mispredict and eat an attack on the way in. It even has the tools to dispatch most Spikes users (who more often than not are weak to Mystical Fire), Toxic Spikes users (who are weak to Psychic) and the large majority of Stealth Rock setters have crud Special Defense.
Or at least that would be the case. Hatterene is also cripplingly slow, slower than most entry Hazard setters not named Ferrothorn, and will likely eat an attack from them. Hatterene's typing doesn't help either. Fairy Psychic is so awkward. You have a Psychic type that is weak to Poison moves, and a Fairy type that gets hit hard by Dark moves, worsening Hatterene's matchup against both types, while only possessing Resistances and Immunities to Psychic, Fighting and Dragon. Having a hard losing matchup against Excadrill, who in addition to the Steel STAB has Mold Breaker to invalidate Magic Bounce doesn't help matters either. Lack of Reliable recovery is another crippling flaw, having only Draining Kiss for recovery means that it is possible and probable to wear Hatterene down faster than it can recover. Hatterene can also do nothing about Entry Hazards already set -so having it as your only answer to them is ill advised as once it goes down, or you mispredict, you are going to be on the back foot for the rest of the battle.
Hatterene does have its benefits. A Trick Room setter immune to Taunt is always welcome and Hatterene can shutdown attempts to cripple by Status hard. 136 Special Attack is phenomenal, and Hatterene has a wide enough movepool for near perfect Neutral coverage.