Elder Scrolls - Morrowind

Refill health level
During the game play, push the B button to get access to the inventory
screen. Press L or R trigger to change to the stats screen. Highlight
"Health" selection and push Black, White, Black, Black, Black, then
hold the A button to restore your health.

Refill magicka level
During the game play, push the B button to get access to the inventory
screen. Press L or R trigger to change to the stats screen. Highlight
"Magicka" selection and push Black, White, White, Black, White then hold
the A buttons to restore magicka.

Refill fatigue level
During the game play, push the B button to get access to the inventory
screen. Press L or R trigger to change to the stats screen. Highlight
"Fatigue" selection and push Black, Black, White, White, Black, then hold
the A buttons to restore fatigue.

Maximum health, magicka, and fatigue levels
First enter the "Refill magicka level", "Refill fatigue level" or "Refill
health level" codes. When holding the A button to filling your
fatigue/magicka/health up, hit the B button before reach the top level
then exit, but keep held the A button.

Increase any type of weapon skills
Bind that type of weapon and hold X + L + R buttons simultaneously.
You will hear a switching sound, but it will not actually switch.

Increase Armor skill
Find and defeat some weak enemies (like Slaughterfish) to increase your
armor skill.

Increase Athletics skill
Run around until your fatigue level will be empty. Then, wait for your
fatigue level to raise to the maximum and then run again.
Note: Run, do not walk!

Increase Block skill
While using a shield and get hit by enemies, hold Chop to increase block
skill.

Increase Mercantile skill
Purchase anything for bargain price (10 to 20 gp) and always go down
on the price slightly. After, sell it back for a little more than
they desire.