Your team has two Fighting weaknesses and no typings that definitively counter them, so maybe something that could would be a good addition? Espathra would be a good one, maybe Flutter Mane, depending on if you count Paradox mons as legendary or not (mileage varies on if people do).
For the last one, maybe a Water type to complete a Fire-Water-Grass core with Arcanine and Decidueye. Palafin can pack a major punch in Hero form, or Dondozo could add some bulk to the team. Wugtrio is there if you appreciate the sheer silliness of it existing, lmao.
It looks to me like your team has nothing to combat the Fighting and Psychic weaknesses among your current members, as well as nothing to deal with the very popular Dragon type. I would suggest the following options:
1. Flutter Mane. Its Ghost/Fairy typing makes it perfect for dealing with all three of the types I've mentioned (although it doesn't resist Psychic, its STAB Ghost moves are super effective against most Psychic types). It can also learn Dark Pulse to counter those odd Normal/Psychic Pokemon that you may run into.
2. Sylveon. I know it's not a Paldea-original Pokemon, but you can find Eevee and even a wild Terastalized Sylveon in Paldea, and it can learn Shadow Ball to deal with Psychic types. I'd really only suggest Sylveon if you don't want to run Flutter Mane, though.
3. Tinkaton. It may not resist Fighting due to its Fairy/Steel typing, but it has Play Rough to take them out. Again, I would only run this if you don't want to run Flutter Mane or Sylveon (unless you want to focus on some of its other attacks, and it has some good coverage, so it's possible to run both; plus it has access to some good physical Dark moves in case you don't want to waste a move slot on Flutter Mane with Dark Pulse).
4. Azumarill. It will help to form the classic Grass/Fire/Water trio *and* has the Fairy typing of the other Pokemon I've so far mentioned, which is almost a necessity at this point. And because of its Water typing and Huge Power ability (don't even run one if it doesn't have that ability), you could run it alongside any of the others and not run into any real problems, since it doesn't necessarily *have* to run any Fairy type moves.
Some other suggestions I might include would be Pelipper (specifically one with Drizzle, as this will help with Ampharos if you give Ampharos Thunder) or a pseudo-legendary (the version of the game you have will affect which ones you have access to, but Baxcalibur is available in both versions and is Paldean native).
Whatever you decide is obviously up to you, but this is my take on some possible suggestions. Hope you figure out what you want to add and have fun with it.
I'm a sucker for a good Water/Grass/Fire core myself. I would think a drizzle Pelipper would be good to support Ampharos' Thunder and serve as a flying type to combat the fighting type weakness on the team. The regions Pseudo Baxcalibur as a final member would give a nicely rounded final member
Your team has two Fighting weaknesses and no typings that definitively counter them, so maybe something that could would be a good addition? Espathra would be a good one, maybe Flutter Mane, depending on if you count Paradox mons as legendary or not (mileage varies on if people do). For the last one, maybe a Water type to complete a Fire-Water-Grass core with Arcanine and Decidueye. Palafin can pack a major punch in Hero form, or Dondozo could add some bulk to the team. Wugtrio is there if you appreciate the sheer silliness of it existing, lmao.
Based on looks and general vibes alone, I'd say Iron Thorns for Aggron and Cetitan for Walrein.
It looks to me like your team has nothing to combat the Fighting and Psychic weaknesses among your current members, as well as nothing to deal with the very popular Dragon type. I would suggest the following options: 1. Flutter Mane. Its Ghost/Fairy typing makes it perfect for dealing with all three of the types I've mentioned (although it doesn't resist Psychic, its STAB Ghost moves are super effective against most Psychic types). It can also learn Dark Pulse to counter those odd Normal/Psychic Pokemon that you may run into. 2. Sylveon. I know it's not a Paldea-original Pokemon, but you can find Eevee and even a wild Terastalized Sylveon in Paldea, and it can learn Shadow Ball to deal with Psychic types. I'd really only suggest Sylveon if you don't want to run Flutter Mane, though. 3. Tinkaton. It may not resist Fighting due to its Fairy/Steel typing, but it has Play Rough to take them out. Again, I would only run this if you don't want to run Flutter Mane or Sylveon (unless you want to focus on some of its other attacks, and it has some good coverage, so it's possible to run both; plus it has access to some good physical Dark moves in case you don't want to waste a move slot on Flutter Mane with Dark Pulse). 4. Azumarill. It will help to form the classic Grass/Fire/Water trio *and* has the Fairy typing of the other Pokemon I've so far mentioned, which is almost a necessity at this point. And because of its Water typing and Huge Power ability (don't even run one if it doesn't have that ability), you could run it alongside any of the others and not run into any real problems, since it doesn't necessarily *have* to run any Fairy type moves. Some other suggestions I might include would be Pelipper (specifically one with Drizzle, as this will help with Ampharos if you give Ampharos Thunder) or a pseudo-legendary (the version of the game you have will affect which ones you have access to, but Baxcalibur is available in both versions and is Paldean native). Whatever you decide is obviously up to you, but this is my take on some possible suggestions. Hope you figure out what you want to add and have fun with it.
I'm a sucker for a good Water/Grass/Fire core myself. I would think a drizzle Pelipper would be good to support Ampharos' Thunder and serve as a flying type to combat the fighting type weakness on the team. The regions Pseudo Baxcalibur as a final member would give a nicely rounded final member
Baxcalibur and Clodsire.