Heatran

Fire / Steel typing combined with base 130 Special Attack makes Heatran a huge threat in Doubles OU. Heatran has powerful spread attacks, mainly Eruption, that hit most of the metagame hard, only needing Earth Power as a coverage move. Its typing and ability also allow it to check common Pokemon such as Amoonguss, Rillaboom, Metagross, and Naganadel. Despite these strengths, its lack of Speed and weakness to common offensive types make Heatran hard to justify in a team, along with facing competition from Volcanion and Incineroar as the Fire-type of the team. Heatran also gets easily threatened by common Pokemon such as Landorus, Urshifu-R, Tapu Fini, Kyurem-B, and Zygarde while also needing caution against Rillaboom and Metagross variants that often carry Ground coverage. Therefore, Heatran fits best on offensive teams, since it provides immediate damage and needs speed control to make up for its subpar Speed tier. Partners that can threaten Fire-resistant foes pair well with Heatran, such as Urshifu-R, Rillaboom, Zygarde, and Kyurem-B. Psychic-type spam deserves a special mention, since it appreciates a powerful Fire-type that can threaten Rillaboom and Steel-types, and it has Necrozma as a possible speed control option with Trick Room. Naganadel is also a great partner for its ability to check some of Heatran's best checks, such as Zygarde, Urshifu-R, and Tapu Fini, while providing Tailwind as speed control.