You'll want someone who can take some ground moves and since Pachirisu is, frankly, useless I would replace him. You don't have an ice weakness and although you do have a Fairy type Klefki isn't actually weak to Poison or Steel. So you can add in Togekiss who makes a great in-game Special Attacker and also someone who can tank a lot of hits.
That and you're attackers are fairly balanced so Togekiss should fit nicely.
In-Game set:
Togekiss @ Whatever-Floats-Your-Boat
Ability: Serene Grace
EVs: 252 SAtk / 252 Spd or HP / 4 SDef
Modest (if 252 HP) or Timid (if 252 Spd)
- Air Slash
- Thunder Wave
- Aura Sphere
- Shadow Ball / Flamethrower / Extrasensory
Competitive set:
Togekiss @ Leftovers
Ability: Serene Grace
EVs: 252 HP / 252 SDef / 4 SAtk
Calm Nature
- Air Slash
- Thunder Wave
- Roost
- Aura Sphere / Defog