WARNING: This articles contains major story SPOILERS for Pokémon Ultra Sun and Ultra Moon. If you care about experiencing these games’ stories unspoiled, you may not want to continue. On the other hand, if you don’t care about the story too much and just want know how to get past this part of the game, then read on.
One of the most difficult battles, if not the most difficult battle, in Pokémon Ultra Sun and Ultra Moon is the battle with Ultra Necrozma in Ultra Megalopolis. If you haven’t gotten to this point in the game yet, you may be wondering how a battle with just one Pokémon could be so hard. Let me explain: Ultra Necrozma has extremely high stats, especially in Attack and Special Attack, and it has an aura that boosts all of its stats even more. It also has a very diverse moveset, consisting of Photon Geyser, Smart Strike, Power Gem and Dragon Pulse. Between these four attacks, it’s likely that Ultra Necrozma will have a Type advantage against a good amount of your team, and super effective moves are powered up even more by its ability Neuroforce. In short, there’s a good chance that Ultra Necrozma has a high enough Speed to attack first against most of your party, will likely have a move that’s super effective against most of your party members and has a high enough Attack and Special Attack that even if there isn’t a Type advantage, Ultra Necrozma is likely to one-shot most of your team. It’s very possible that you’ll lose to Ultra Necrozma without even getting a single hit in. By the way, you can’t catch Necrozma during this battle, so all you can hope to do is defeat it. Luckily, I came up with a strategy that is almost guaranteed to help you beat Ultra Necrozma, even if your team isn’t that good.
Simply put, there are two specific things you need for this strategy: Mimikyu and TM06 Toxic. Many of you can probably figure out where I’m going with this with just that information, but for those of you who aren’t as familiar with specific Pokémon mechanics, allow me to explain. Mimikyu has a unique ability called Disguise, which basically acts as an automatic Substitute at the beginning of every battle. When Mimikyu gets hit with an attack for the first time, the Disguise will take the hit instead and Mimikyu will not take any damage. After this, the Disguise is “busted” and Mimikyu will take damage regularly. Basically, all this does is ensure that Mimikyu will get at least one move in at the beginning of each battle. For this strategy, that one move is all we need.
If you’re with me so far, you’ll want to go catch a Mimikyu. There are two ways to do this. One is by wandering around inside the abandoned market that is now the site of Acerola’s Ghost Trial, just south of Tapu Village. Mimikyu has about a 5% spawn rate, so it may take a little while to find one. The other way to get a Mimikyu is by getting the Totem Mimikyu from Samson Oak. To do this, you will need to have collected at least 80 Totem Stickers. If you are having a hard time finding Stickers, you can refer to our guide by clicking here. Once you have 80, go talk to Samson Oak at Heahea Beach and he’ll give you a Totem Mimkyu.
The next thing you’ll need is TM06, which teaches Pokémon the move Toxic. You can find this TM at Aether Paradise by going to the dock level and traveling all the way to the bottom left of the area, where you’ll see it lying on the ground. Toxic is a move that can be learned by almost any Pokémon for some reason, but we’ll want to teach it to Mimikyu, since its Disguise ability assures that it’ll be able to use it before Ultra Necrozma knocks it out. Teach your Mimikyu Toxic and make sure you have a full team of six Pokémon. Don’t worry about grinding Mimikyu up so it’s at the same level as the rest of your party; Ultra Necrozma will probably be faster than it anyway, so no need to waste your time right now.
The cool thing about Toxic is that it not only poisons your opponent, it badly poisons them. There’s a difference. Regular poison removes 1/16 of your opponent’s overall health every turn, whereas bad poison damages your opponent by 1/16 on the first turn it’s afflicted with the status condition, then adds another 1/16 of damage every turn they remain badly poisoned. This means that the first turn your opponent is badly poisoned, they’ll take 1/16 damage, the next turn it’ll take away 2/16 of their overall health, then the next turn it’ll take away 3/16, etc. until they are defeated or cured of the poison.
So what you’ll want to do is have your Toxic-using Mimikyu at the front of your party. Save in front of Ultra Necrozma before interacting with it just in case this doesn’t work (Toxic has 90% accuracy, so there’s a small chance that you’ll miss, in which case you’ll want to just start over). Use Toxic on your first turn. In all likelihood, Ultra Necrozma will out-speed your Mimikyu and attack first, but the damage will be taken by Mimikyu’s Disguise, so Mimikyu will still be able to get the Toxic in. The first turn will end with Ultra Necrozma badly poisoned, so it will take 1/16 damage, reducing its health to 15/16. From here on out, you’re pretty much guaranteed to win no matter what you do. Even if Ultra Necrozma proceeds to sweep your entire party, you’ll still win, just as long as all six slots in your party are filled up. On the second turn, Ultra Necrozma will probably take out your Mimikyu, but it’ll take 2/16 damage from the poison, reducing its health to 13/16. Next, Necrozma will take out your second party member, then poison will reduce its health to 10/16. Necrozma will beat your third party member, its health will reduce to 6/16; Necrozma will beat your fourth party member, its health will reduce to 1/16; finally, Necrozma will beat your fifth party member and the poison will take Necrozma out. With one party member still healthy, you’ve won the battle.