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https://www.pokemonpets.com/Shiny-Mega-S...edex-10791

With the update of generation 7 pokemon added to pokemonpets came the addition of this beast!

It's abilities are: Attack Master, Expert Regenerator and Physical Master. Attack master increases the attack stat by 30% , Expert Regenerator heals the pokemon HP by 15% at the end of the turn and Physical Master increased the base power of physical moves by 30%.
As we can see, none of these abilities are detrimental to Shiny Mega Solgaleo, they all benefit this pokemon .
Best nature(s): Adamant, Brave, Lonely, Naughty 

Shiny Solgaleo itself has base 171 attack and base 171 hp and when you perform a mega transformation on this pokemon it's base attack goes up to a crazy 246 base attack! which is 21st highest among pokemon in this game.

The primary role of MS (mega shiny) Solgaleo is to be a bulky physical attacker so the most common moveset seen is :

Sunsteelstrike (has 1000 accuracy and stab with base power 100)
Iron head/ Metal Burst (iron head has 30% flinch/cringe chance and Metalburst is base power 90 stab)
ZenHeadbutt (has 20% cringe/flinch chance and stab base power 80)
Earthquake  (base power 100 physical all-around good ground attack)

Morning Sun and Flareblitz are also honorable mentions. 
This set has all physical attacks so the abilities all benefit MS-solgaleo. Some of the attacks also offer and opportunity to cringe/flinch your opponents pokemon, then you get to attack again. 

Team Synergy/Role flexibily: Solgaleo is a psychic/steel type which is great both offensively and defensively but has a glaring weakness against strong fire, ground, dark and ghost types as such recommended team mates includes a strong water type preferable bulky such as SM Milotic , SM vaporeon or SM kyogre. For dark and ghost types , a strong special attacker is recommended such as SM Magearna. A stat debuffer also pairs well with solgaleo, such as sm lugia, sm umbreon. They both help the breaking ability by reducing vital stats such as accuracy which helps solgaleo dodge moves and recover more easily.

Solgaleo can also fulfill a role as a boosting attacker/wall breaker. 
Moveset: Work up/Hone Claws, Protect, Metal burst/Return, Sunsteelstrike

This moveset boosts Solgaleo stats while breaking holes in the walls against your opponents team. It is particularly tricky to takedown because of expert regenerator.

Popular items used on this pokemon are attack weapon(increases attack stat in battle), steel/psychic orb (recovers hp at the end of your turn) or razor claw which increases the base power of physical moves in battle.

It's easy to see why this pokemon is so popular in ELO and PVP usage and how easily it can sweep through your opponents team.