Heatran

Heatran's typing coupled with Flash Fire grants it important immunities and numerous key resistances. This allows it to come in on a plethora of bulky Pokemon such as Eternatus, Ho-Oh lacking Earthquake and Xerneas and wear down opposing teams with its strong movepool. Its signature move, Magma Storm, allows Heatran to trap and KO many of the tier's special walls such as Eternatus, Ho-Oh, and Blissey in combination with Taunt. Utility moves like Stealth Rock, Roar, and Toxic can help further break down bulkier teams and allow teammates like Groudon to forgo support moves in favor of more offensive sets. Unfortunately, Heatran's lack of reliable recovery limits the number of teams it can work on and forces it to rely on Leftovers, which makes it extremely vulnerable to the common Knock Off and entry hazards. Its typing also comes with various weaknesses to common attacking types, which requires extensive team support. Finally, Magma Storm's accuracy and low PP make Heatran somewhat unreliable at what niche it does have.