Magearna is easily one of the best Pokemon in the formats that allow it. It has many attributes that make it a great Pokemon. Great Movepool, Great Ability, Great Typing, Great Stats, and the rest!
Positives:
+ 130 Sp Attack is great by any standards
+ Soul Heart is one of the best abilities in doubles. This allows Magearna to snowball very well
+ Steel/Fairy is arguably one of the best typings in the game
+ 80/115/115 is pretty good bulk
+ It's movepool is top-notch. For a strong Fairy move, you got Fleur Cannon, you also got Flash Cannon, Aura Sphere and others.
+ It looks like a Diancie and a Klinklang had a baby. And one awesome one at that.
Negatives:
- 65 Speed isn't that good. Magearna does have a way to boost it with Shift Gear but even with a boost, it can still struggle to outspeed targets
- Steel/Fairy is great, but your 2 weaknesses are very common. This can lead to issues against certain targets.
- FMSS is an issue due to a giant movepool.
- Due to being a Mythical, it isn't allowed in certain formats such as VGC so using one can be limited
Abilities:
Soul-Heart: Possibly one of the most broken doubles abilities in the game. In singles, it's bascially a Special version of Moxie, which is good and all but in doubles, you get the boost of any Pokemon faints, including allies and you don't necessarily have to KO with Magearna to get the boost. This ability can make Magearna very dangerous at times.
Counters: Heatran is faster and can usually deal with Magearna, however a boosted Aura Sphere or Focus Blast can lead to trouble. Landorus T/Zygarde can also deal back great damage with an Earthquake/Thousand Arrows. Essentially, go with a faster Pokemon with a Fire or Ground move and don't let Magearna get its boosts.
