In Baten Kaitos 1 each character has their own deck with cards that are used to act in battle: attack, defend and items (healing items, buffs, camera, etc). At the start of the game you can only use two cards on your own turn, but this gradually increases with Class Up. When defending you can defend each hit with one card.

You can change target and you can target your own characters. When you want to heal your characters, remember to target them, otherwise you may accidentally heal the enemy.

Each card has 1 to 4 numbers at the corners, at the start of the game most of your cards have only 1 number. You can choose which of the numbers is used when you attack. Your attacks get a percentage bonus when you get pairs, multiple of the same numbers or get numbers in order.

Here are some examples of numbers in order that give you a great bonus. They can go in reverse order too. The most powerful attack turns are when you can do 9 attacks that have numbers in order (from 1 to 9, or 9 to 1).

• 1 + 2
  
• 3 + 2 + 1
  
• 5 + 6 + 7 + 8

Getting pairs gives you a smaller bonus. Each number must have at least one of the same kind in the chain, but they do not have to be in order. Pairs are easier to get, but their bonus pales in comparison to the above.

• 2 + 2
  
• 1 + 1 + 3 + 3
  
• 7 + 8 + 7 + 7 + 8

Here are some attack chains that do not give any bonus:

• 4 + 5 + 7 + 6 (numbers not in order)
  
• 3 + 3 + 5 + 7 + 7 (number 5 does not have a pair)

At any blue save flower you can teleport to the church. The man at the altar can give you both Level Up and Class Up.

Level Up is earned with exp points from battles and it upgrades character stats. Characters earn exp points even if they are not used in battle.

Class Up can be earned only with special Class Up items unique to each character. These are found in major dungeons and boss battle rewards. Class Up raises the card limit of your deck, allows you to play more cards per turn and shortens the turn timer.

(Mild spoilers: list of characters who will join the party.)

Most of the characters have access to all of the six elements, except for Lyude (light and dark) and Savyna (fire and water), but each character has 2 or 3 elements they are best at (more attack cards and finishers with that element).

Some characters attack faster (they spend less time on each card and start the attack faster). This does not affect damage or enemy block chances, faster characters are just harder to play as because you have less time to choose cards.

• Slow: Xelha, Lyude, Mizuti
  
• Medium: Kalas, Gibari
  
• Fast: Savyna

You can play the characters you like and clear the game with no problems, but if you want an easy but powerful party then I recommend utilizing either Xelha or Mizuti for elemental damage, Lyude for raw damage (and light/dark) and then anyone you like as the third member.

Xelha and Mizuti are not completely interchangeble because they focus on different elements with their finishing moves, but you can use either one in most situations.

In my experience, Lyude is the best damage dealer in the game and you only need to switch light/dark around which makes his deck easy to manage. He has a wide variety of neutral attacks and his light element attacks help with many tough boss fights. His cards are easily available and very strong.

Here is a quick blueprint for a deck, but do some testing on your own.

• 1-4 healing items depending on how high the card limit for the deck is, at least 1 that can resurrect fallen party member.
  
• 1 camera, maybe 2 if fighting a boss with multiple targets.
  
• 2-4 finishers.
  
• 1/3 armor cards (1/4 for Kalas and Gibari because they can defend with attack cards too).
  
• Rest of the cards are attack cards and maybe some useful item cards.

Adjust your party composition and elemental attacks depending on the level. At the endgame I usually have the best damage dealer only have attacks and finishers to maximize damage and one character that can heal a lot. Once you can play 6+ cards per turn it's usually better to deal a lot of damage instead of blocking a lot of damage.

You can see elemental bonus damage on the result screen after each attack. Usually enemies of an area have one or two major elements they use and they are weak to the opposite element (for example, river has water creatures that are weak to fire). As the game progresses, enemies and bosses have multiple types. Element pairs are:

• Fire - Water
  
• Wind - Earth
  
• Light - Dark

Performing a combo, playing two or more specific cards in specific order, creates a new card that can be chosen as the reward after the battle. If you have created a Prophet's Notebook (play Blank Notebook, then Magic Pen), all combos you create will be saved into the collection menu.

These cards vary from very useful to useless, some are required in other combos. Some simple combos can be guessed, some have tips on how to create them in dialogue and some you just have to look up on the internet.

If you need help with combinations, you can check this guide on Steam:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3375416218