Hey, all! I've been lurking in this thread for a while as I've been working on getting all the gold symbols, and I'm happy to report a couple streaks on retail. I only have a general idea of my Pokemon's IVs (I just bred until I got a correct-natured baby with "quite impressive" stats or better), so I've just listed EVs and actual stats for each one.
Battle Dome Open Level (Level 60): 12 Championships
Houndoom @ Charcoal - "Brimstone"
EVs: 6 HP, 252 Sp. Attack, 252 Speed
Stats: 177 HP, 116 Attack, 80 Defense, 191 Sp. Attack, 117 Sp. Defense, 191 Speed
Ability: Early Bird
Nature: Timid
Sunny Day, Flamethrower, Solar Beam, Crunch
Bellossom @ Lum Berry - "Kahuna"
EVs: 252 HP, 252 Sp. Attack, 6 Speed
Stats: 214 HP, 96 Attack, 117 Defense, 181 Sp. Attack, 141 Sp. Defense, 76 Speed
Ability: Chlorophyll
Nature: Modest
Sunny Day, Solar Beam, Moonlight, Sludge Bomb
Swampert @ Leftovers - "Gillian"
EVs: 252 HP, 252 Sp. Defense, 6 Attack
Stats: 243 HP, 154 Attack, 131 Defense, 112 Sp. Attack, 173 Sp. Defense, 79 Speed
Ability: Torrent
Nature: Careful
Curse, Earthquake, Rock Slide, Return
Strategy
This team was a little challenging to use, but I had a lot of fun with it. Curse Swampert was the MVP, able to steamroll opponents easily once it set up--it was one of my choices for almost every battle. Houndoom was great for dealing with the grass types Swampert was highly allergic to and for revenge killing if Swampert (or, on rare occasions, Bellossom) ever went down. I gave it a Charcoal, but I'm not sure whether that made a meaningful difference to Flamethrower's power. I mostly just wasn't sure what to give it, so I thought Charcoal might be handy for situations where I didn't have time to set up the sun. Bellossom was pretty tanky thanks to its Special Defense investment and excellent at eliminating bulky water types, which Swampert usually had a little trouble with. It could consistently survive one super-effective special attack from them (usually an ice-type move) while using Sunny Day and then one-shot with Solar Beam on the next turn with the Chlorophyll speed boost. Lum Berry ensured that it could strike back even if it got frozen or paralyzed while waiting to set up the sun. Bellossom could also stall with sun-boosted Moonlight if necessary, but I only relied on that when I was in a pinch.
Funnily enough, even though Swampert was my most reliable team member, I left her behind for the gold symbol battle. Tucker brought Latios and Swampert, which I beat with Houndoom and Bellossom, respectively. I don't remember all the details of my loss, but it was in the final battle of my 13th round. I think I lost Swampert to a critical hit Cross Chop from a Machamp and couldn't recover after that. Frustratingly, the other Pokemon was either Aggron or Metagross, both of which Swampert could've taken down easily!
Battle Pike Open Level (Level 60): 163 Rooms
Skarmory @ Leftovers - "Maverick"
EVs: 252 HP, 6 Attack, 252 Sp. Defense
Stats: 202 HP, 118 Attack, 185 Defense, 60 Sp. Attack, 157 Sp. Defense, 92 Speed
Ability: Sturdy
Nature: Careful
Toxic, Protect, Drill Peck, Roar
Flygon @ Choice Band - "Nabooru"
EVs: 252 Attack, 6 Sp. Attack, 252 Speed
Stats: 183 HP, 179 Attack, 102 Defense, 109 Sp. Attack, 104 Sp. Defense, 199 Speed
Ability: Levitate
Nature: Naive
Earthquake, Rock Slide, Hidden Power Bug, Fire Blast
Miltank @ Lum Berry - "MaryMooCow"
EVs: 252 HP, 6 Attack, 252 Defense
Stats: 236 HP, 114 Attack, 204 Defense, 56 Sp. Attack, 100 Sp. Defense, 134 Speed
Ability: Thick Fat
Nature: Impish
Earthquake, Body Slam, Milk Drink, Heal Bell
Strategy
This was a solid team for Battle Pike, with every member playing a role in facing several of the different events. I used
this guide on Reddit to inform my room choices (shoutout to Snicker40 over there), which basically led me to avoid non-healing single battles as much as possible. Skarmory was useful for wild Pokemon rooms and status rooms thanks to its poison immunity, and it was great for stalling out tanky threats in hard single battles with the time-honored Toxic/Protect/Leftovers combo. Flygon was great for dealing damage in single and double battles, especially through the classic flying-type/Earthquake strategy in doubles. It was a little hard to switch into sometimes during single battles because of its relatively low bulk, but its speed made it a great revenge killer. Miltank was the cleric, armed with a Lum Berry in case the whole team ever got hit with sleep/freeze or if she got hit with a status move while trying to Heal Bell her teammates. I probably would've preferred to use Blissey if I had access to trading (I have a copy of FireRed, but I lack the hardware necessary to trade), but Miltank ended up being a helpful backup for Flygon in double battles thanks to its good physical attack, so it worked out well.
Going into the gold symbol fight, I was mostly only worried about Gyarados, who threatened to destroy my whole team with Rest and Dragon Dance. Flygon took care of Seviper and Steelix fairly easily, and then I just stalled Gyarados a little bit so Flygon could come in while it was Resting and take it out with two Rock Slides. I don't remember the details of the loss that ended the streak, but I'm almost positive it was during a hard single battle.
All in all, I've been having a lot of fun with the frontier. I'm not going for huge records or totally optimal Pokemon (as you might be able to tell, lol). I'm just trying to come up with fun teams that I like for each facility, refining them as necessary to win gold and then seeing how far they go after that. I'm going to keep working on the rest of the facilities, so I'll hopefully have more to share soon!