>>58819010Garchomp uses either Focus Sash or Yache Berry to live an Ice move.
Excadrill likes Focus Sash because it guarantees you can get off two attacks.
Kangaskhan is only used for the Giga Impact meme, so Normal Gem is a better item.
Ampharos is usually a mono-attacker with Thunderbolt and screens, so Magnet or Shuca Berry are better than the mega stone.
Gyarados can be mega, but it usually likes being Flying type to 1v1 Garchomp and Excadrill, so Wacan or Life Orb feel more common in my experience.
Then you have Golisopod, Clefable, Baxcalibur and Gallade, where the mega is about as much stronger as a Life Orb, so it comes down to whether you want immediate power or the invincibility frames from mega evolving.