Rewards

A number of rewards can be set for each achievement. Simply list them within an achievement with a unique Reward parent section:

Crafts:
  diamond_sword:
    1:
      Message: The first time you crafted a blade!
      Name: craft_1_blade
      DisplayName: Blacksmith Apprentice
      Reward:
        Money: 2
        Experience: 100
        Command:
          Execute: give PLAYER 158 10

You can also give rewards when a player has received all achievements! Use the AllAchievementsReceivedRewards configuration section like this:

AllAchievementsReceivedRewards:
  IncreaseMaxOxygen: 30
  Experience: 100

Money

If you have Vault and an economy plugin, you can specify:

Money: 1

Item

Use a Material name:

Item: diamond 1

If you want a custom name for your item, add it at the end:

Item: stone 5 Tombstone

Experience

Simply:

Experience: 100

Max oxygen

30 corresponds to one bubble added to the oxygen bar:

IncreaseMaxOxygen: 30

Max health

Simply add 1 heart to the player's health:

IncreaseMaxHealth: 1

Custom command(s)

Put the command in Execute. Display will be the displayed description of the command:

Command:
  Execute: "say §7ALERT: §4PLAYER§7 has become the §4STONE GOD§7!"
  Display: Become the Stone God!

You can omit the Display parameter, in which case list-reward-command in lang.yml will be used:

Command:
  Execute: give PLAYER 158 10

You can chain several commands by separating them with a ;:

Command:
  Execute: give PLAYER 158 10; give PLAYER 126 5