With the release of the Teal Mask DLC comes a lot of new tools and changes for Metronome Battles. Let's take a look!
ITEMS
Technically the Fairy Feather now exists to boost Fairy moves, but we already had the Pixie Plate which will probably be better to Fling. There are also some Ogerpon items for form changing.
MOVES
We get some new moves and some returning moves in the pool.
Returning Metronome-eligible moves include Tail Glow, Dark Void, Seed Flare, Forest's Curse, Toxic Thread, Clanging Scales, and Take Heart (Refresh + Calm Mind). There are a lot of pretty impactful moves, and also Dark Void which is still useless to anyone who isn't Darkrai.
In a surprising twist, every new DLC move is callable via Metronome! Blood Moon is a 140 BP special Normal move that can't be used twice in a row (I don't know what would happen if you randomly called this twice in a row), Matcha Gotcha is a 80 BP 90 accuracy special Grass move that restores 50% HP and can burn, Syrup Bomb is a 60 BP 85 accuracy special Grass move that lowers the target's Speed for 3 turns, and Ivy Cudgel is a 100 BP physical Grass move with high crit and changes type for Ogerpon formes.
ABILITIES
We have a few new abilities. Mind's Eye combines Scrappy's ghost hitting with Keen Eye's accuracy protection and evasion ignoring. I don't think this is immune to Intimidate so base Scrappy may still have a niche if you see a lot of Intimidate teams while laddering. Supersweet Syrup lowers enemy evasion on entrance, which is kind of bad compared to Compound Eyes because it will activate Defiants and get blocked by any stat debuff protection. Hospitality heals the ally on entrance which is useless.
Toxic Chain adds a chance of bad poison on any attack. I do not know the exact chance at this point but I expect it to be between 10 and 30% like Poison Touch, and currently on PS they have it as 30% which is pretty scary. As I've discussed earlier this is pretty game changing and could be meta defining, but there are ways around it including being Poison or the Covert Cloak item.
Embody Aspect is largely tied to Ogerpon's gimmick and I don't know if it fully functions on anyone else, but it's basically 4 abilities that boost Speed/SpD/Attack/Defense, so we could have an Intrepid Sword for everything but SpA. On Ogerpon itself it functions rather differently which I'll explain in the Pokemon section. Also this ability technically doesn't have Intrepid Sword's drawback of only activating once per battle but this may only matter for Skill Swap and I don't know if it can be swapped.
POKEMON
Dipplin (Grass/Dragon) is an Applin evolution and so it has a middling 485 BST with a spread of 80/80/110/95/80/40, which is still in the realm of being usable by dumping speed. What's more intriguing is that it can use the Eviolite which has more implications for DLC2.
Sinistcha is yet another Grass/Ghost, this time a clone of Polteageist which shares its exact stats of 71/60/106/121/80/70 (508 BST). It does end up as the Grass/Ghost with the highest SpA stat and decent bulk, but also has the lowest Attack of them all which can be a problem.
Okidogi is a Poison/Fighting type with a 88/128/115/58/86/80 (555 BST) stat spread. It's a fair cut above Toxicroak and Sneasler mostly with its Defense and a fair amount of resistances, but a 4x Psychic weakness is always looming for it and it has a lot of competition trying to be Fighting type or just physical.
Munkidori is a Poison/Psychic type with a 88/75/66/130/90/106 (555 BST) stat spread and ends up rather comparable to Galarian Slowking, who makes up the difference in BST by being weaker but much slower and also bulkier. As a type, Poison/Psychic is arguably worse than regular Poison but still better than Psychic alone, and they end up cancelling out some weaknesses and resistances between them to be left with 3 weaknesses and 4 resistances.
Fezandipiti is a Poison/Fairy type with a balanced 88/91/82/70/125/99 (555 BST) stat spread. Compared to Galarian Weezing it wins in HP, Attack, SpD, and Speed. Poison/Fairy at least has some better synergy with 5 resistances + 1 immunity and double resisting Bug and Fighting but still isn't the best. At the least, all these Poison types are still immune to Toxic Chain.
Ogerpon is a weird mon to theorize about, because there are multiple hardcoded aspects to it that are unclear to know how it will work in this theoretical environment. It has several formes that are either Grass, Grass/Rock, Grass/Fire, or Grass/Water, and the latter 3 may require a hold item to use, but I'm not sure if this will or will not be the case in Metronome which would be a shame. Its base stats are always 80/120/84/60/96/110 though, which is decent for a Grass legendary. Notably, its tera type is locked to match the type of its current forme due to its form change mechanic, and
apparently the game softlocks if you try hacking another on it, so that already limits its options, but it gets stranger.
Ogerpon's main gimmick is that it has regular abilities other than Embody Aspect to start, but when you terastallize, you change into the tera form and automatically have the respective Embody Aspect ability to boost a stat. This is basically the modern version of mega evolving to change your ability. I'm not sure if this can still activate if hacked on base Ogerpon, but I guess you could use it in base to double up on a stat boost, or just run Intrepid Sword/Dauntless Shield for a similar effect.
Overall Ogerpon may end up relatively limited in terms of its options in Metronome depending on how things go, since it will be the only mon physically unable to go Tera Ghost, and it may also have to give up its item slot for its formes and also lose the Grass type and have to run a temporary ability if you want to use its tera gimmick on top of that. If not, I guess you have some more physical Grass options to work with, but you could also just tera Abomasnow or something. Things may go differently in practice, but for now I feel like Ogerpon may just be too limited in its options to stand out in a meta where anyone can run anything. It's an unfortunate debut for a Grass legendary headlining the DLC.
EDIT: This may be changed later, but currently all of Ogerpon's formes do lock you into their tera type but you can use them with any item. Here's me stacking all the Attack I can get and still being weaker than Mega Heracross while being forced to tera into a Fire type. Maybe I should just go Intimidate.
EDIT 2: I did realize now that unlike the Mega version, you can actually make use of Magician as your initial ability to steal an item since it's tera-based and not item based. So that's something unique Ogerpon can do, but your second ability is still locked to a raw stat boost.
EDIT 3:
Choosing Ogerpon-Hearthflame-Tera and terastallizing makes you an
unmon that has no stats. Don't do this.
Also anything that transforms into Ogerpon apparently is not able to tera themselves for what it's worth.
EDIT 4:
I forgot to talk about Ursaluna-Bloodmoon despite talking about its ability and move. It's Ursaluna, but as a special attacker instead with a 113/70/120/135/65/52 spread (555 BST) that has a still respectable attack stat but sacrifices some HP and SpD as well. This could be an alright mon with its balance and currently is tied for the highest SpA among Normal-types. Physical may be more common and useful as seen by the failings of Darmanitan-Zen using it as a dump stat, but having viable mixed offenses is pretty good too.