Bukkit

An outcome section can have two optional sections - drop_chances and exp_chances. Use these if you want to override the mob's default drops and experience (they don't need the list format because an outcome section can only have one of each):

mobs:
  - name: pig
    conditions:
      - outcome:
          exp_chances:
          drop_chances:

The exp_chances section takes a list of chances, each having a percent, exp, and optional replace_exp (default is yes) value:

exp_chances:
  - percent: 10
    exp: 100
    replace_exp: no
  - percent: 50
    exp: 20

The drop_chances section takes a list of chances, each having a percent, replace_drops, exclusive and drops section:

drop_chances:
  - percent: 50
    replace_drops: no
    drops:
      - {id: 89}
  - percent: 50
    drops:
      - {id:17}

Put it all together and it looks like this:

mobs:
  - name: pig
    conditions:
      - outcome:
          exp_chances:
            - percent: 10
              exp: 100
              replace_exp: no
            - percent: 50
              exp: 20
          drop_chances:
            - percent: 50
              replace_drops: no
              drops:
                - {id: 89}
            - percent: 50
              drops:
                - {id:17}

In this example, every pig that died, no matter how, would have a 10% chance of giving 102 exp (100 + the 2 original exp), a 50% chance of giving 20 exp (replace_exp is true by default), and a 40 % chance of giving 2 exp (the default).

It would also have a 50% chance of giving 1 Glowstone (plus any pork chops) when it died, and a 50% chance of giving a block of wood.