Hippowdon @ Leftovers
Ability: Sand Stream
EVs: 252 HP / 240 Def / 16 SpD
Impish Nature
- Stealth Rock
- Slack Off
- Earthquake
- Whirlwind
CM Mega Latias is a good setup sweeper and defensive check/counter to common Pokemon like Keldeo and Tangrowth. However, threats like Tyranitar, Tapu Koko, Garchomp, Mega Charizard X and others threaten to either trap, gain momentum on, or set up on Mega Latias.
Mixed Hippowdon is a great partner for Mega Latias. This Hippowdon set reliably sets up hazards, which in conjunction with Sand damage and Whirlwind provide valuable chip damage that let Mega Latias sweep late game easier. Hippo also can counter answers and threats to Mega Latias like Banded Tyranitar, Mega Charizard X, all Tapu Koko, non-Bloom Doom Heatran, and Scarf Garchomp, threatening them with Earthquake or setting up Stealth Rock while avoiding the 2HKO from anything, even after SR damage. Because Hippowdon has reliable recovery, it can do this multiple times per match. Hippowdon also checks or can phaze out (with Whirlwind) threats to Mega Latias like Mega Pinsir, SD Hawlucha, Scarf Latios, Mega Diance, Offensive Landorus-T, Scarf Tapu Lele, Mega Scizor, Volcarona, Zygarde, Mega Lopunny, CM Clefable, and Mimikyu. Often times, the chip damage Hippowdon gets with EQ on the latter threats is enough to let Mega Latias muscle through after only one Calm Mind boost.
In return, Mega Latias answers and/or sets up on Hippowdon's enemies like Keldeo, Tangrowth, Mega Venusaur, Mew, Mantine, and Mega Sableye. This core is still susceptible to powerful wallbreakers like Kyurem-Black, Fairium Z Magearna, (Ash) Greninja, and Kartana. It also has a hard time breaking through Celesteela, Ferrothorn, and Toxapex, without any boosts on Mega Latias. So, when teambuilding, make sure to account for those mons as well.