Descriptions below are copied/pasted from irowiki site.
Perfect Dodge:
Every character starts with a value of 1.
10 luk increases your Perfect Dodge by 1.
Perfect Dodge allows the player to dodge a physical attack by a chance in % corresponding to the Perfect Dodge value.
It is calculated before FLEE hence why it is not reduced by the mob effect, that is to say when a player has several monsters attacking him.
Flee therefore triggers after the fact that a player lucky dodged something or not, thus giving him even more chance to flee a monster. This part of the flee is reduced by the mob effect.
It does not work against skill attacks, traps, or magic.
This overrides (potential) critical hits.
Note
Homunculus' flee is similar to this, as it is not reduced by the mob effect.
Flee:
Flee is a character's ability to avoid being hit by regular attacks and most melee skills. The more Flee a character has, the less likely they will be hit by an attack. Generally considered to be the counterpart to DEF/VIT. Flee does not affect being hit with some magic attacks and some skills. Flee is determined by (Level + AGI).
Being attacked by more than one monster decreases your Flee by 10% per every additional monster. This reduction is counted before adding Flee from Skills that directly add Flee (ie. Thief's Improve Dodge). This means that if you are attacked by 4 monsters and your Flee is 150, your Actual Flee would be 105 assuming that you don't have any Flee from any skills directly. This also means that if you're attacked by more than 10 monsters at the same time, they will always hit you regardless of your Flee.
