Negative levels? How do they work and how can you apply them quickly?

[Schiffer]

As title asks.

[My Self]

For each negative level, -1 to any d20 roll, -1 to level-dependent class features, and -5 HP.

Level-dependent class features are things like caster level, Smite Evil, Sneak Attack, and Rage rounds (but not rage STR/CON bonuses). There might be a few odd corner-case d20 rolls that don't qualify, but most do.

[Andy Brown]

On the prd glossary page just over half way down (Energy Drain and Negative Levels)

approximately: apply -1 to all rolls, and -5 hit points to current & maximum, for each negative level. Then treat as the appropriate number of levels lower than normal for level dependent effects.

[CalethosVB]

Enervation, 4th level Sorcerer/Wizard spell. Gives 1d4 temporary negative levels for 1 hour per caster level, maximum 15 hours. Negative levels gained through this spell have no chance of becoming permanent unless you have a way of extending the duration to 24+ hours.

There's other ways, such as some undead having abilities to grant negative levels.