I started off playing this tier as a joke, but I found that there was legitimately interesting strategy in teambuilding for the tier, so here is the team I found to be the most consistent when laddering.
Pokestar Spirit @ Choice Band
Ability: Magic Bounce
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
Brave Nature
- Metronome
Celesteela @ Choice Specs
Ability: Flash Fire
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
Quiet Nature
- Metronome
I decided to choose one of each of the strongest combinations in the tier, Ghost/Dark and Steel, to avoid being completely blown out by counter strategies such as Pixilate or Mold Breaker. Both pokemon are equipped with Choice items, as I believe that the immediate 50% boost provided by Choice items is more consistent than Weakness Policy (as I deliberately minimised the super effective moves that both pokemon were vulnerable to) and provided more upfront power than Metronome (needing 5 turns to gear up is a significant disadvantage). One of each Choice item diversifies the damage my team does, and helps vs pokemon really fat on one side of the spectrum such as Slowbro-Mega or Registeel.
Both pokemon run maxed out EV's with a positive nature for their main attacking stat and a negative nature for speed, as speed is usually not very useful in the format. I considered minimising speed for both to answer Perish Song, but the utility in forcing a speedtie vs other Pokestar Spirit/Celesteela was ultimately more useful (I won every Perish Song game I encountered with Celesteela anyway).
Pokestar Spirit @ Choice Band
Ability: Magic Bounce
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
Brave Nature
- Metronome
From the Ghost side, Pokestar Spirit is by far the strongest legal ghost type in the format with 100 stats all around, so it's inclusion was a no-brainer. I opted for Magic Bounce to help counter things like Taunt/Torment and status moves, as well as the plethora of debuffing status moves present in the format. I also tested out things like Defiant and Magic Guard, but I found Defiant was too inconsistent, requiring both a status drop and for Metronome to roll a reasonably strong physical attack (while not helping vs non stat drop moves). Magic Guard was inferior to Magic Bounce in almost all ways and was ultimately less consistent, helping only in the Flame Body matchup.
Celesteela @ Choice Specs
Ability: Flash Fire
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
Quiet Nature
- Metronome
For my steel type I went for Celesteela due to having the best stat spread out of the legal steel types. Scizor-Mega lacked special attack, while Genesect lacked bulk.
I decided to run a type immunity ability, in order to reduce the number of games I lost to the opponent rolling multiple super effective moves. Out of Lightning Rod and Flash Fire, Flash Fire was chosen for its consistency over Lightning Rod.
In Metronome Battle, Fire type attacks are both more powerful and more common, while also having more spread moves. I found that Flash Fire activated in the majority of my games, while I could go multiple games without seeing an electric move. Celesteela is also able to abuse opponent Lightning Rods and Delta Streams, meaning that in a signficant amount of games its Electric weakness is nullified anyway.
Overall, I found that out of the games I lost a significant number were due to self-killing moves or Imprison, for which there is no real counterplay to at current. While Metronome Battle is mostly a joke format, its still really fun and has interesting teambuilding decisions.