Torkoal -> 4
Dumb li'l turtle getting Drought means it's like Zard-Y for Trick Room, but because it gets Eruption and has a free item slot, its spread move hits harder.
252+ SpA Charizard-Mega-Y Heat Wave vs. 0 HP / 4 SpD Landorus-Therian in Sun: 267-315 (83.6 - 98.7%) -- guaranteed 2HKO
252+ SpA Charcoal Torkoal Eruption (150 BP) vs. 0 HP / 4 SpD Landorus-Therian in Sun: 325-384 (101.8 - 120.3%) -- guaranteed OHKO
Besides that, it's surprisingly chunky physically, notably taking even Life Orb Landot and surviving, albeit barely.
252 Atk Life Orb Landorus-Therian Earthquake vs. 252 HP / 0 Def Torkoal: 260-307 (75.5 - 89.2%) -- guaranteed 2HKO
It puts up some respectable numbers, 2HKOing low-bulk fire resists and almost OHKOing Tapu Lele with no investment.
252+ SpA Charcoal Torkoal Eruption (150 BP) vs. 0 HP / 0 SpD Salamence-Mega in Sun: 148-175 (44.7 - 52.8%) -- 26.6% chance to 2HKO
252+ SpA Charcoal Torkoal Eruption (150 BP) vs. 4 HP / 0 SpD Tapu Lele in Sun: 241-285 (85.4 - 101%) -- 12.5% chance to OHKO
Steels are basically pronounced dead on arrival, less resilient things like Koko and Hoopa-U are OHKOed, and everything takes a lot. It takes some of the bulkiest Waters in the tier to not get at least 2HKOed by Eruption.
252+ SpA Charcoal Torkoal Eruption (150 BP) vs. 252 HP / 0 SpD Azumarill in Sun: 164-193 (40.5 - 47.7%) -- guaranteed 3HKO
252+ SpA Charcoal Torkoal Eruption (150 BP) vs. 252 HP / 0 SpD Tapu Fini in Sun: 108-128 (31.3 - 37.2%) -- 83.4% chance to 3HKO
252+ SpA Charcoal Torkoal Eruption (150 BP) vs. 252 HP / 0 SpD Milotic in Sun: 112-132 (28.4 - 33.5%) -- 0.2% chance to 3HKO
Unlike Zard-Y, Torkoal gets Sludge Bomb and Earth Power to go with Solar Beam as coverage moves, so it isn't totally thwarted by them either. My calcs use Charcoal specifically so it isn't choice-locked, but it can run Specs for yet more punch if the partners can handle them. For teammates, it of course demands big Trick Room support, and it also needs friends who can get bulky fire resists. It's not hard to plan for that though, 'cause it's easy to tell which of the top-tier guys are the ones that take Eruptions.
It is astonishingly slow, and needs Trick Room to do pretty much any work. Alternate weather effects really dig into its damage output, and if it gets chipped it has to rely on a less exciting Heat Wave. Both really show off how 85 base special attack is actually pretty bad. 70/70 special bulk is meh, slightly less than Tapu Koko. As a special-based sun sweeper, Zard-Y answers will almost always get to it too. The level of investment to get this dumb turtle in there is pretty significant, but I believe the payoff earns it a spot in the situational niche tier, as it can score some KOs with Eruption that Zard-Y can't with Heat Wave and make the most of the short duration of both TR and Sun.