I've been using Eternatus and spamming Necro-DM since the start of the ladder and even got reqs for the suspect test with them, so I wanna give my thoughts on both of them since quziel brought them up.Dragalge,
Necro-DM,
Kyu-W,
Eternatus are all mons that probably need more experimentation.

Necrozma-Dusk-Mane @ Leftovers
Ability: Prism Armor
Shiny: Yes
EVs: 252 HP / 4 Atk / 252 Def
Impish Nature
- Stealth Rock
- Toxic / Thunder Wave
- Knock Off
- Morning Sun
I've found this to be its best and most consistent set (shoutout Discordual). NDM can survive a single hit from just about every threat in the meta with its incredible bulk, typing, and ability. This means that you're almost guaranteed to either 1) Knock Off an item 2) Get up Stealth Rocks or 3) Toxic something. A lot of my success with NDM comes from using it as a pivot on Balance. Bring it in on a choice locked Pokemon, Gardevoir or Gallade for example, and survive a single hit then switch out into something that can take advantage. A lot of the popular support or glue Pokemon don't threaten NDM, so for the most part you're safe to bring it in and either heal up or click any of your other 3 moves. Conversely, you cannot do much to them either once you've removed their item or gotten up SR. Status is a bit of a 50/50 as well since a lot of the popular blobs don't mind Toxic from you, which was why I tried to use T-Wave instead. I ended up switching back to Toxic anyways since I prefer the residual damage it provides. I experimented with a strange double status set with T-Wave and Toxic with Wish support from Umbreon to keep it healthy. Very mixed results I'd say. Its best MU I'd say is against stall teams since virtually nothing on their team threatens you, and you can be an absolute nuisance by spamming Knock Off or Toxic while maintaining SR constantly. Its toughest MU I would say is Ferrothorn. Bringing NDM into Ferrothorn is almost always to your detriment even if you remove its item. It's practically guaranteed a free Leech Seed or hazard when you're in, and attacking it usually hurts you more than it hurt it. I've had games where Ferrothorn would be 20% but claw its way back up to 40% or 60% because I'd stay in with NDM to reset SR or Morning Sun. Corviknight is also a tough MU as well for obvious reasons. Something that could help the MU is going -Spd with 0IV's to get a Knock Off or Toxic off on whatever they bring in. I would say that NDM is proven to be a great option from my experience. Definitely bring something that can come in on Ferrothorn though.

Eternatus @ Metronome
Ability: Pressure
EVs: 252 HP / 80 SpA / 176 Spe
Timid Nature
IVs: 0 Atk
- Recover
- Sludge Bomb
- Flamethrower
- Toxic Spikes / Toxic
I've likely been using Eternatus wrong, so this probably the furthest thing from its most optimal set or spread. It serves a similar role to how I use NDM where it's a bulky pivot that I bring in. It is a lot less bulky but much much quicker. My best use of it was to use it to Pressure stall, namely on Umbreon or to waste Heal Bell/Aromatherapy PP. Just like NDM, it likes MU against really bulky teams. The name of the game was to slowly annoy teams by spreading Poison and slowly chip at them while burning their very limited PP. Eternatus does not have the damage to threaten a lot of the bulkier mons in this tier, so Metronome is there to further pressure mons for trying to stay in on you. I'll bring up the Umbreon example again. You don't do enough damage to threaten it, so Umbreon is free to stay in and Wish/Protect then Heal Bell on you without much care. This gets a lot harder with the combination of Metronome boosts and potential poisons from Sludge Bomb along with Pressure that will make them a lot less comfortable staying in on you. It does this a lot less effectively to Corviknight since you're also losing PP from their Pressure. Also like NDM, it has great MU's into a lot of the tier's blobs save for Noivern or Toxapex. Clefable, Ferrothorn, Corviknight, Umbreon, Slowbro/King, Tangrowth to name a few do not pose a threat to you besides Knock Off, so it's very easy to bring Eternatus in on them and do something annoying like set up T-Spikes or Recover. Toxapex is this thing's worst MU by a mile. You don't threaten it with anything in the slightest besides just staying in to Pressure stall, but you're also burning your PP doing so. The opposite is also true where they can't do much to you as well, and Eternatus can absorb the T-Spikes that Toxpex might sight up on you. Besides that, I think it's quite great against offense as well. The offensive typing and Speed lets you shred a lot of popular offensive mons like Garchomp, Togekiss, or Tsareena depending on your coverge, and if they can't deny or remove T-Spikes, then they're in for a rough time. Eternatus likely needs more experimentation, but I do think Pressure stalling + hazard stack is a very viable way to use Eternatus.
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