You can forge weapons as well, but you can't vary the parameters by more than a certain amount total. It is sometimes cheaper than investing in a new weapon and other times it is more expensive but a much more effective weapon comes out of it. It is also useful for training weaker units that start with a weaker weapon and need more power and accuracy to help kill the opponents. You are allowed to forge as often as you want but money is always an issue for forging.
Furthermore, there are Support conversations. This gives the characters a ton of depth in terms of personality and character development and most units can support with most other units. These supports add to double boosts, add to the chance of getting a Dual Attack or Dual Guard, and they add to various other things like Dodge, Evasion, Hitrate, and Critical rate when your unit is adjacent. It is very useful and it is good to get as many supports as possible so your units are as flexible as possible. Some units can also fall in love and get married, too!
Each unit is assigned to their own class. Your main character, Chrom, has the "Lord" class which has solid bases and growths, can use Swords, and has some skills associated with it. As you progress through the story, once a character reaches around Level 10 (max Level is 20) they can be promoted, like in traditional Fire Emblem games, and gain stat boosts, extra weapons, some abilities, etc. In this game, you gain stat boosts relative to your class bases; basically, if you want to promote from a Cavalier to, say, a Great Knight, then you lose a point or two of Speed because a Great Knight's Speed is a little lower than a Cavalier's. On the flipside, they gain a huge amount of Str and Defense.
However, classes used to be little more than just some sort of aesthetic thing for each character. This game is considerably deeper with classes. There are three brands of classes - "unpromoted," "promoted," and "special" classes. Unpromoted classes can use Master Seals to promote, promoted classes cannot promote further, and special classes have a Level cap of 30 instead of 20. However, they also learn skills at different rates.
This game reintroduces the concept of Skills from FE4/5/9/10 and Tearring Saga. Every class has its own individual skills that it learns at varying levels. Unpromoted units learn them at Level 1 and Level 10, promoted at Levels 5 and 15, and special classes at Levels 1 and 15. So that is a grand total of four skills except... wait a moment...
Like in FE8, every unpromoted class (except Lord) has two classes it can promote to. These two choices are often balanced; sometimes you're trading speed and certain skills for an extra weapon and some defense (Cavalier -> Great Knight or Paladin), or you're sacrificing monstrous Str/Def/HP for Speed/Swords/Movement (General and Great Knight). The choice is yours to make in the end but it does decide a lot of things. If that is not enough, if you did not like your promotion selection, then what oyu can do is level up to Level 10 as a promoted unit and use what is called a Change Seal... which changes the unit's class to something else. It doesn't promote them or anything. But every unit has a pool of 3 classes to choose from.
So Chrom can be a Lord, Archer, or Cavalier and all of their promotions; so his full class selection is Lord, Great Lord, Archer, Sniper, Ranger, Cavalier, Great Knight, Paladin. He can Master Seal and Change Seal indefinitely (if unpromoted, he must be Level 10; if promoted, he can Change Seal at any moment but can only Change Seal to other promoted classes at Level 10, until then he can only Change Seal to unpromoted classes). He can learn all of their skills and everything.
The skills aren't like they used to be. There's not as many "% chance to attack 5 times in a row" or "% chance to nullify defense" like we used to have. There's a few others, like "Recover 50% HP when you kill an enemy on Player Phase," "Once per turn, move again if you kill an enemy on Player Phase," or even something as simple as "Heal 5 more HP when you are healing another unit." There are around 40 classes with 2 skills each and every unit has access to an average of 10-15 skills, so you have a lot of options and paths to choose from. Be warned that if you are picking up a new weapon due to a class change, you are restricted to the "E-rank" weaponry. So if Chrom class changes to an Archer, then he will start with E Bows because he hasn't used Bows prior. If he class changes to Cavalier, then he is likely to retain a high Sword rank (because he uses Swords as a Lord) but he has E Lances.
Like FE8 we have a world map. We can visit any point of this world map and buy items from their shops or confront enemies that have taken the space. However, these enemies are entirely optional if they have taken the space; you do not have to fight them but you cannot buy items from them until you fight them and defeat them. Thankfully, you have an option to go back to the world map if you enter a level completely overwhelmed and unable to beat it or enter a map battle unable to beat it. This game would be annoying otherwise.
Unless you find out how to break this game in two, it is a fairly difficult game. Without pair up it is extremely difficult because you have no way of getting the stat gains that help you beat other enemies down. With pairing up, it can be a lot easier but it requires more planning (for instance, if you have a healer, there are less units on the field so the healer is far more exposed than they would be normally). Normal Mode is not too difficult generally, Hard Mode has some difficulty spikes that happen at points (but get easier), and Lunatic makes Hard Mode look like My Litle Pony. Some classes can trivialize this game easily, as well as some weapons and skills, whereas if you aren't keeping up with the fandom or anything the game gets to be difficult. Even despite all of this, enemies will hit hard no matter what mode you are on; it just matters with what accuracy they hit you with. Doesn't matter how broken your units are because they will manage to find a way to hit hard.
When units die they die forever. You can restart a level or map to get that unit back, but you lose all progress because you are starting from the last time you saved effectively. You can save in the middle of a map but it's only a quick save type of thing, where you can shut off your game and load that save again (but then the save is gone).
If that doesn't tickle your fancy, then there is a "Casual" mode. The above is known as "Classic" mode. In Casual mode, if a unit loses all of their HP, then at the end of the map or chapter they come back to your party unscathed, with all their equipment, and with the same level ups as before. Chapter saves are now more like permasaves, where you can save before you make a decision then reload if you didn't like it or whatever, exactly like a save state. This is great because if you didn't like Classical Fire Emblem stuff then the Casual version will make it considerably less irritating for you. I know it was an integral part of the game for a dead unit to be gone forever, but that's why
I play Classic (and you can too if you like that!). Others play Casual because, well, it's a less irritating game and irritating games can be boring and tedious after a while.
While there is a World Map that you can continue to mess around with after you beat the game, there is also paid DLC which has maps with pretty good design. They can range from very easy to incredibly difficult like the later ones, and they give you new items, classes, and characters. I'd say a select few items are worth it, but that's about it. You may also want to buy some of them for the story, since they have one that treats all past FE games as Spirit Characters that are trapped in some sort of weird limbo and another one about the bad future. Also, they have one that is basically a swimsuit paradise, but sadly the localized version has a slightly censored version of that. If you've got more DLC questions then shoot away!
Also a very replayable game. ~40 characters, many different class trees and one more feature that I will not go into (if you get the game you will see for yourself) that creates a ton more variety.
The music in the maps is absolutely beautiful and it has very powerful melodies combined with a more serene ambiance. There are also two versions of all map themes; one for the map itself and one for when you enter battle and watch animations. To see the effect,
here (also contains a lot of gameplay information if you want to skim through his videos; I can look for specific timestamps upon request of different things I describe, as well as different videos - don't worry, you can skip animations and the fact that the game cuts away to battle). Two of my favorite pieces are known as
Destiny and
Duty. There are some throwback pieces in there; for some reason one of them is a mixture of Ike's Resolution from Fire Emblem: Path of Radiance... and that is actually my all-time favorite track in this game (but I don't think many of you would like it), but I want any FE9 fans to find it in the game and listen to it and feel what I felt (which was mind numbing joy). The expedition theme for map battles against the Risen is a remix of the Fire Emblem Main Theme, also pretty cool.
From here I'll have Lottie take over and talk about the game from her point of view. I avoided plot almost entirely because I was not pleased... but my expectations are unrealistic as hell.