Roll additional hit points. This is based on hit dice found in your class table plus your constitution modifier. If the rolled number is lower than your old HP total, increase the old number by one and take it instead.
Improve your attack bonus. This is also based on your class table.
Improve your saving throws. At level 1, the base number for all saving throws is 15. Each additional level decreases the base by 1. The new base number is still modified by your attributes. |New Saving Throw| = 16 - |Current Level| +- | -Attribute Modifier |
Gain and spend Skill Points. Each level you obtain 3 skill points to spend on either skill levels, or attribute increases.
Skill Points can be used immediately after leveling up.
If you choose to save Skill Points, you can use them later, with approximately a weeks delay in the effect.
Level-4 is the maximum level for skills.
Choose new Foci. Some Foci provide bonus skills. This acts differently during leveling than during character creation. Each Foci bonus skill acts as +3 Skill Points.
Leveling choices are generally permanent. Exceptions are in-story great powers, or if a character choice is significantly troublesome to the party or character.
You cannot change your choices for the sake of “optimization”.