In second place we have Zacian. This is one of the best Pokémon ever as it is an incredible attacker with a great moveset and ability to compliment its role. It does have some limitations that are the reason why this Pokémon got second place, and we will go more in depth in all of these factors.
Zacian has a base stat total tied with Arceus, the creator of the Pokémon universe. It has an effective base stat total of 640, better than Arceus and other Pokémon like Mega Rayquaza. It has a phoenomonal attack stat of 170 and an amazing speed stat of 148. It has a good 115 defense and special defense which is really good for a Pokémon and its only bad stat is its HP which is 92, but is still alright. Its special attack doesn't matter since it is a physical attacker.
Zacian is an amazing wallbreaker and attacker in general. It learns some great moves that compliment this playstyle as well, some of its best are down below.
Behemoth Blade is a 100 base power steel move that deals double damage to dynamax Pokémon and Play Rough is a fairy type move that has 90 base power and has 90% accuracy as it's only drawback. Close Combat is a 120 base power move that lowers the user's defensive stats. Close Combat is good as it can deal good damage to fire and super-effective damage to steel types, which are resisted by both fairy and steel types. What makes even better is that the most common fire type is Incineroar, which is weak to fighting moves. Swords Dance is always a nice addition to physical attackers as it raises your attack stat by two stages when used, but on this Pokémon, you don't exactly need that attack boost since your ability does that for you.
Intrepid Sword is probably the stupidest decision ever, since this Pokémon gets a one stage attack boost, or a 1.5 times multiplier to its attack. For those of you who don't understand how insane this is, it basically has a 255 attack stat unless its attack is dropped.
Zacian has arguably the best type combination in the game. It is Fairy/Steel, which gives it the best defensive type combined with the best offensive type, this gives it two weaknesses of ground and fire. It also has immunities to poison and dragon. This is great for Zacian as this makes up for its mediocre bulk.
The Pokémon Company gave us some remorse and decided to give it some nerfs before we even got to play with it for the first time in Generation 8. Zacian has two nerfs that in the end, are why I put it below the number two Pokémon. First is that it can't hold an item, unlike the #1 Pokémon. This is terrible as if Zacian could hold choice items, life orbs, or anything that could benefit it, that would make this Pokémon even more scary, which we don't need. The other nerf is that it can't dynamax, but this doesn't hurt it as much as it would become damaged double by other Zacians and it would lose the bonus effect of Behemoth Blade for three turns, but there are cases where you would want to dynamax it, which is not good when there isn't the option.
Zacian was nerfed in Generation 9, right after it was introduced, because of how strong it was. Dynamax no longer exists, meaning Behemoth Blade has no bonus effect. It also was nerfed to lose 20 attack from its base stats, and it also was nerfed so Intrepid Sword only activates once. That worked and now this Pokémon is irrelevant. At one point, however, this Pokémon was like no other.