Magmortar @ Firium Z
Ability: Vital Spirit
EVs: 252 SpA / 4 SpD / 252 Spe
Timid/Modest Nature
IVs: 0 Atk
- Sunny Day
- Fire Blast
- Focus Blast
- Solar Beam/Thunderbolt
Sun makes Fire Blast stronger, and Z Sunny Day boosts this thing's Speed by one, which makes it pretty effective at busting through some of the faster, but frailer, checks and supporting the rest of the team, or cleaning up later on.
edit: forgot to mention that it can also be used to turn fire blast into a nuke if you don't want sun or smth