Double Strike - Increases the chance of double attack. (20% chance for double hit)
Intent - Chance to land critical hits. (9.9% + 0.1% per CA level chance)
Envenom - Adds poison damage to Frenzied Rampage. (2.8% + 1.4% per CA level)
Vampire - Chance for the Shadow Warrior to leech from the target and add them to his own hitpoints. (2 + 1 per CA level) - This works exactly the same as Life Leeched per Hit +X and is modified by Tactics Lore, but not by +% Damage.
Tactics Lore - indirectly, it increases weapon damage and critical chance, thus making Frenzied Rampage hit harder. Also increases the life leech damage of the Vampire modification and allows for modification points.
Any weapon lore (such as Hafted Weapons when the Shadow Warrior is wielding an axe) - will indirectly increase this combat art's execution speed, damage and chance to hit, and will allow the equippng of higher level weapons used to execute this combat art.