Why are there so many choice items? I understand Greninja, I see it on Lando-T (but having both is a little over the top), And Magnezone benefits from Air Balloon much more than a Scarf.
Like PX ™ said, Regice is a bad Pokemon; there are other Mons that do Regice's job better.
Aysu (Tapu Fini) @ Fightinium Z
Ability: Misty Surge
EVs: 252 Spe / 150 Def / 106 SpD
Calm Nature
- Defog
- Taunt
- Focus Blast
- Moonblast
AYSU f Turkish
Derived from Turkish ay meaning "moon" and su meaning "water".
Anat (Greninja-Ash) (f) @ Choice Scarf
Ability: Battle Bond
EVs: 252 Atk / 252 Spe / 4 HP
Jolly Nature
- Hydro Pump
- Dark Pulse
- Ice Beam
- Water Shuriken
Anat - "water spring" Semitic Goddess of fertility, hunting, and war worship
Eun-Ji (Landorus-Therian) @ Life Orb
Ability: Intimidate
EVs: 252 Atk / 252 Spe / 4 SpD
Adamant Nature
- Earthquake
- Rock Slide
- Knock Off
- U-Turn / Defog
Eun - "Mercy"
Ji - "Ground"
Although, if you want a Defog-er, I like this Landorus and Greninja core much better.
There is no reason why you should have Rotom set to Wash because you already have Greninja. If your desperate for Rotom, Rotom-Heat will give better coverage because you have no fire type. But, a core that works well with Regice(if you still want to use it) is Heatran.
Cináed (Heatran) @ Air Balloon
Ability: Flash Fire
EVs: 252 HP / 252 Def / 4 Spe
- Earth Power
- Ancient Power / Rock Slide
- Flash Cannon
- Flamethrower / Heat Wave
Cináed - "Born of Fire"
Adding this core with Magnezone or Regice will do you perfectly fine with Flash Fire.
Summary
Rotom-Wash - Switch for Heatran
Lando-T - Kept, change moveset
Greninja - Kept, change moveset
Pinsir-Mega - Kept
Magnezone - Kept, change item
Regice - Possibly switch for Tapu Fini
Overall, good job.