Tactics Lore - indirectly, it increases weapon damage and critical chance, thus making Demonic Blow hit harder. Also increases the leech life effect of the mod 3a Life Leech 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.
Combat Discipline - will increase its damage and reduce its regeneration time if this Combat Art is placed within a combo. This increase in damage is direct; it increases the +xx% that the CA adds to base damage.
Speed Lore - will increase its chance to hit indirectly by increasing a player's attack rating.
Keep the CA level either very high and use it as a one hit wonder to kill off champs and on bosses, and utilize from the high Ca lvl and gain high chance for modification effects.
Or keep it very low and use it as your main attack when other combat arts are on cooldown.
Using regen per hit modifier will allow you to have no regeneration time, so you can land as many Demonic Blows as you want.
Pros and Cons
Strong single target damage, can be modified to attack several opponents through an area of effect mod.
Low regeneration time
Strong boss killer with modifications for wounds and poison debuffs.
Fast execution animation making it viable for a short regeneration time.
The mod 1b Vehemence (area of effect) and the mod 3a Life Leech (enhanced by Tactics Lore) work good together, as you can add to your health a considerable amount of hitpoints with only one hit.
Single target attack, must be modified to attack more than one opponent.
Mod 2a Frailty only reduces opponent's physical armor.
In Ice and Blood, the animations for Demonic blow became broken when the Shadow Warrior used it with the following weapons while mounted on the HellHound: Ranged Weapons, Pole Arms, 2h Magic Staves. This bug was fixed in the Community Patch 1.60.