If you're allowed to ready a move action as a ready action, is it therefor allowed to five foot step and then declare your readied action to move when an opponent approaches?
SRD said:The action occurs just before the action that triggers it. If the triggered action is part of another character’s activities, you interrupt the other character. Assuming he is still capable of doing so, he continues his actions once you complete your readied action. Your initiative result changes.
If readied actions occur immediately prior to the event which triggers them, could a readied action "Move when X opponent swings at me" negate an opponents attack?
Depends on how the GM rules the interrupting works, but many seem to run it that way.If readied actions occur immediately prior to the event which triggers them, could a readied action "Move when X opponent swings at me" negate an opponents attack?
Yes.
But be careful about the AoO you'll provoke when doing so.![]()
I don't believe an AoO can occur in the middle of a swing.
IE: Lv20 barbarian approaches Lv20 fighter, fighter has a readied action to 5 Foot Step backwards as soon as the barbarian makes his first swing.
SRD said:Deciding between an Attack or a Full Attack
After your first attack, you can decide to take a move action instead of making your remaining attacks, depending on how the first attack turns out. If you’ve already taken a 5-foot step, you can’t use your move action to move any distance, but you could still use a different kind of move action.
This would make a character invulnerable to one melee combatant (without Reach), allowing for other PCs to take him down during that time. He would be a very effective tank.

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Rulebook featuring "high magic" options, including a host of new spells.