Crimson Rush is a Vampirism power that makes your active abilities hit harder the healthier you are. It is open from the start, so you only need Corruption and skill points to learn it.
Rest at a road shrine and buy it from the Vampirism tree. It needs skill points and enough Corruption, but no blood phial.
It pays off if you fight carefully and keep your health topped up. If you trade hits a lot, the bonus will rarely be at full strength.
Scarlet Shield heals you after perfect blocks, which helps keep your health high enough for Crimson Rush to matter.
Image: Rebel Wolves / Bandai NamcoBlood Surge
Blood Surge is a night-only Vampirism ability that makes a target burst from the inside through their own blood. You unlock it by drinking Xanthe's blood, so it is tied to her questline.
Compel Soul
Compel Soul is the first Witchcraft hex Coen learns, from Anca, after Laslea is sacked. It makes the recently dead replay the moments before they died, which is how you crack many investigations.
Mesmerise
Mesmerise is a Vampirism power that lets you take control of an enemy's mind. You unlock it with Lacra's blood during The Night of Horrors, so it comes from story progress.
Piercing Shriek
Piercing Shriek is a Vampirism power that stuns enemies with a banshee-like scream. You unlock it with Brencis's blood, either from a phial in Xanthe's Recruiters: Taste of Power or at the end of Our Rotten Roots.