Epic Improved Skirmish( Complete Adventurer, p. 192)
Your combat mobility improves.
Skirmish +4d6/+4 AC,
If the bonus to AC granted when you use your skirmish ability is equal to or higher than the number of dice of extra damage granted by your skirmish ability, your extra damage on skirmish attacks increases by 1d6. If the bonus to AC granted by your skirmish ability is less than the number of dice of extra damage granted by your skirmish ability, the bonus to AC when skirmishing increases by 1 instead.
This feat may be taken multiple times. Its effects stack.
Errata: This feat was originally called Improved Skirmish