Source: Complete Scoundrel
You combine your scout training with the stealth of a rogue to open up new methods of ambushing enemies.
Prerequisite: Skirmish +1d6/+1 AC, sneak attack +1d6.
Benefit: Your rogue and scout levels stack for the purpose of determining the extra damage and bonus to Armor Class granted when skirmishing. For example, a 4th-level scout/7th-level rogue would deal an extra 3d6 points of damage and gain a +3 competence bonus to AC when skirmishing, as if she were an 11th-level scout.
In addition, you can qualify for ambush feats as if your sneak attack bonus damage were the sum of your skirmish damage and sneak attack bonus damage. You cannot sacrifice skirmish extra damage to use those feats, however.
Special: A scout can select Swift Ambusher as one of her scout bonus feats.