Camerupt:
11
Torkoal:
10
Magcargo:
10
Skarmory:
4
Rhyperior:
3
Bellossom:
2
Victreebel:
2
Banette:
2
Hariyama:
2
Togekiss:
2
Volbeat:
2
Dugtrio:
2
Raticate:
2
Golem:
1
Metagross:
1
Shiftry:
1
Kingdra:
1
Weezing:
1
Crobat:
1
Primeape:
1
Octillery:
1
Ludicolo:
1
Pelipper:
1
Machamp:
1
Spinda:
1
Our first "organic" round, as it were. Really interesting mix of species here (both from Game Freak and from the people on this thread).
There were a few different types we could have used for this round but, being so adjacent to (B)D(S)P Fire, I was really interested to see how this Fire would play out. Of course, none of the Fire-type Pokemon in this pool are ones which overlap with those in (B)D(S)P Fire and none are actually from Sinnoh at all so it's a whole different ballgame. Given the Battle Zone's abundance of Pokemon not from Sinnoh, it's perhaps not surprising that more than one person's idea for a team might be someone not from there originally.
So what naturally conflates with Fire? Well, taking into account the characteristics of the area and the logical association with the boiling, scorching power of erupting volcanoes, you're left with a very strong idea of what types of trainers probably thrive here - so it's very easy to go straight for teams composed entirely of rough, heavy, lumbering colossuses. But I was surprised at how many people chose to consciously steer away from this and go for a theme of beauty! Or if not beauty exactly, a gentler take on nature at least - Grass-types, Bug-types, Water-types, even a few Normal-types. Quite taken with these, there were some rather ingenious ideas in play this time.
Camerupt being the most popular Fire-type used by everyone makes total sense: it's a literal volcano in a volcano area so idk how you justify not using it. That leaves Magcargo and Torkoal tied for second. No pre-evos, which isn't really surprising though it would have been amusing to see someone try something funky with Numel.
Of the rest, Skarmory makes sense as the most popular wildcard: it's a Pokemon known for inhabiting harsh, rugged areas, so much so that it's characteristically synonymous with Orre, the harshest and most desolate region we've seen in the series to date. Rhyperior also fits as a wildcard immensely: being a rocky dinosaur, there's a clear visual association with heat and power, and Fire has a lot of dispositional overlap with Rock and Ground. When it comes to Grass-types, Victreebel fits the vibe of the Survival Area perfectly - an aggressive and unpredictable carnivorous plant that can melt you to death or slice you to pieces seems exactly the sort of Pokemon you'd fear to meet as you thrash your way through a stifling rainforest.
Also I love seeing Togekiss used twice, it seems so hugely out of place but... somehow just works?
Stuff I expected to see more (or at all):
Golem. Similarly to Rhyperior, it's a Pokemon associated with steep mountains and has an affinity with Fire and explosions, and has the same tough, craggy vibe many of the other Pokemon around here do.
Weezing. Toxic gases abound in volcanic location (especially in Platinum where the whole area got a much-needed visual upgrade) and Weezing is a Pokemon I recall running into a lot inside Stark Mountain. It and the Magcargo I caught there and used as an egg-hatching aid for years in Pearl are practically synonymous with the location to me. Anyway, Weezing also learns a few Fire moves including the still-fairly-rare Will-o-Wisp - it's always felt like a Fire-adjacent Pokemon to me.
Metagross. Much like Skarmory, it's a resilient metal being associated with harsh environments and while it doesn't have much Fire adjacency, it fits onto a Fire team quite well as there's some good synergy in play. There's particular scope to use Metagross alongside Camerupt since it can make use of Magnet Rise to avoid being hit by Earthquake.
Kingdra. Again, on paper a slightly odd-looking choice, but if you're going to add a Water-type (as several people did) why not one that's a hardy dragon? While it doesn't learn any Fire moves, its shooter-like snout gives it an association with explosive weaponry and it has access to several moves incorporating beams, pulses, blasts, and cannons. The Battle Zone is a place where tough trainers gather and Kingdra is a difficult Pokemon to raise and evolve, so it wouldn't be surprising to see it used by anyone you encounter.
Kingler. But there's also this - the hardiest of crabs. While it's a Water-type, it has a delightfully brutal learnset filled with Rock, Ground, Fighting, Dark, and Steel moves. While crabs are generally thought of as water-dwelling creatures, they also do inhabit jungles and rocky areas, and I think Kingler's spiky and aggressive appearance more than justifies its inclusion in a Battle Zone squad.
Every so often when there's a team concept that seems really obvious to me but no-one touches, and this round is one of those: I was really surprised no-one went for an all-out Explosion team! Nothing says "highly destructive explosive power" quite like a volcano (well... except an actual bomb, that is) and such a high-risk, high-return strategy is well within the profile of the earthy, brash, hard-as-nails sorts you can imagine making their living in the Survival Area. On the other side of the coin, there's also that one cowardly Hiker in Mt Ember who'll teach the player Explosion.
Fittingly, there's a bunch of Pokemon in this area who learn Explosion and/or Selfdestruct. Camerupt, Torkoal, and Magcargo can all detonate themselves, and from the other native Pokemon of the area we've got Shiftry, Golem, Weezing, Wailord, Forretress, and Metagross. Explode away while your teammates use Protect, Endure, or Dig to avoid the blast (or nothing at all in the case of the bulky Rock- and Steel-type squad members) and enjoy watching your foes fall like dominoes.
Speaking of high-risk, high-reward strategies, something else occurs as I write this: OHKO moves. Camerupt and Torkoal both get Fissure, and there are more than enough Pokemon in the area to add a wide variety of other OHKO users: Pinsir, Kingler, Wailord, Seaking, Walrein, Golem, Dugtrio, Hippowdon, Rhyperior, Whiscash. Definitely could work. The only other archetype I can think of is an obsessive Heatran hunter who's crazy about Fire and Steel Pokemon and has fittingly assembled his team in an even split to reflect his passion: three Fires, three Steels. There are just enough Steel-types in the area to allow this: Metagross, Skarmory, and Forretress.