New amiibo
The 3.0.0 and 3.0.1 patches have been recently released, as well as the addition of Ken to the amiibo metagame. With Pichu incoming, this is the list of amiibo fighters currently in the metagame, courtesy of somebody in the scene whose name I can’t remember:

On top of Ken, Joker is now a playable character. Which is cool, except that there’s no amiibo for him, so he doesn’t have much of an effect on the metagame yet. Keep your eyes peeled for a Joker amiibo.
Balance patches
The entire list of balance changes is here, but we’ll point out a few important changes. Across the board, Nintendo has nerfed the damage that projectiles inflict on shields, making shields generally safer at a distance. It doesn’t affect every projectile but affects most of them, and there are a few important projectiles that have been nerfed.
- Mii Gunner’s missile (Side Special 3) is the absolutely most optimal move in his entire moveset. It’s fallen under this nerf, meaning that amiibo can be taught to shield against this move. It’s a medium nerf to Mii Gunner as an amiibo. His C variable has decreased, and this is the largest individual change to the amiibo meta.
- King K. Rool’s crown, but not his cannon, has also been nerfed in this manner. This is a minor nerf, as the crown hits twice anyway and will probably hit the opponent nonetheless. His reduced vulnerabilities in other areas more than make up for this nerf. His C variable has arguably increased, depending on how he’s trained.
- Mii Swordfighter’s projectiles, Neutral special 1, 2, and Side special 3 have all been nerfed on shield. Mii Swordfighter’s signature move, Gale Strike (Neutral special 1) is their best asset: it deals lots of damage, really eats at shields, and knocks the opponent vertically for easier killin’. Well, it doesn’t eat shields as well anymore. The same goes for the Chakram, his Side special 3. While the utility of the Chakram depends on the stage, it’s now worse on shield as well. That presents a moderate problem for the Swordfighter, but it’s not a major one. His C variable has decreased, depending on moveset.
- Olimar’s signature move, his Pikmin Throw, has been nerfed on shield. Thank God. Olimar’s C variable has decreased, but not that much.
Aside from these changes, (the list is quite long), there are three universal changes. The first is that multiple perfect shields can no longer be activated when only one parry was inputted. While that’s sort of a nerf against Piranha Plant’s side special, it’s a bonus in every other circumstance. Your downtime is reduced to the downtime of a single parry, thankfully.
Characters are now penalized for continuous dodging, which has arguable effects on the meta. From what I understand, this effect is only a few frames worth, so it’s not worth looking into.
When someone parries against a projectile, the resulting downtime has been shortened. That is actually a somewhat important change, especially once we figure out how to reliably get amiibo to parry. Until then, this is still an important change for amiibo that fight projectile opponents.
Stages
Two new stages have been added in the 3.0.0 update. Well, technically, only one stage has been added: Mementos. Mementos is a cross between Final Destination on the right side and Battlefield on the left, and it will be added to the hazardless ruleset for ASMR tournaments. It’s an unorthodox stage, but it functions basically the same as Battlefield without the right-hand platform, so it’ll be included.

The second stage is one that we’ve already had but haven’t been able to include. It’s also my favorite stage, and thanks to Nintendo doing a bit of backend work, it now functions just fine. Fountain of Dreams has been optimized to be completely lagless in both hazards and hazardless versions, and will also be added to the ASMR ruleset soon.

There’s one more major change in the 3.0.0 update, but it might not affect the amiibo metagame. Nintendo has added the meme-rich Stage Builder, which gives us the ability to produce our own stages. That sounds totally awesome at first.
However, I don’t expect that the addition of Stage Builder will change a lot. Amiibo tend to have a hard time with custom stages, even when they’re supposed to be recreations of existing, simple ones. Ledges aren’t easily turned off, and as far as I’m aware there’s no way to make simple pass-through platforms. While Stage Builder has a lot of potential to expand the stage list, I don’t believe we can utilize it just yet.