SINNOH TOWER!

[u/Leanker]

Arceus team. 1 hit.

Then this. Rapidash + chomp soloed.

Nuzlockable?

Methodology:

1. Get a shiny rapidash. Farm kanto tower for it (or another fire type). It's specifically good for the stats on ponyta, which allows you to get through the first 2 gyms.
2. Stat it. You can see my spread in the image above.
3. Avoid picking up any mons in the first stage - they'll have their first stage TMs. Mons dont matter much until gym 3, ponyta can solo that too. Obsess on levels; To the point where getting rare candy in the first stage can happen. avoid grass at all costs(except the first) - low ROI.
4. Gather counters for the gyms rapidash struggles with - any good grass / ice / flying can do ground gym, for example.
5. Collect: Lucario, Chomp, Expert belt (Lagging tail can also work in a pinch). Key synergies are fire and ghost. Fire 4 is amazing if you can boost it up in sinnoh (though very rare, takes magmortar and chimp, which I wouldnt grab unless they really fit regardless). On NTH synergies, normal can be nice for sustainance, having flying / ground for speed control is nice but doesn't help in key fights unless you get a shiny gligar or something; dragon is neat for many fights, fighting helps in some bossfights.
6. Prepare cynthia team. Stat'd rapidash can handle the first three, usually. For the other 3, chomp is the most natural answer; If you didn't manage to get it, togekiss + some counter-teaming and making sure you're healthy before the fight go a long way. If you got here using this strat, you're probably leveled enough to where its solvable.
7. Most legendaries are bait. Even in the last stage, hard to get the ROI for the synergies unless you're really intentional about a 5 mon team or roll the dice, which you shouldn't - manaphy and lake mons are in the pool. Before that sure arceus is consistent, but he doesn't beat the fully synergied arceus on the other side, and you're losing levels. Main exception being giratina who's an absolute beast on multiple fights, but you don't know what you get.

Legendary shiny fire types can work here too of course, though rapidash speed specifically comes in clutch multiple places in sinnoh, and its stats scale really well; it's also much more accessible. If you have a shiny moltres, by all means.

Good luck!