The hex Spirit Shackles will cause the afflicted to deal a large portion of their damage to their victim's mana instead of health.
A portion of damage from the victim affects mana instead of health.
For example, the cursed player or monster might deal 30 damage with a scimitar or blast of fire - and the recipient of that attack will take 20 damage to their health and 10 to their mana, assuming they have enough.
Experienced mages may recognize this as a sort of reverse Mana Shield. In this case, the witch does not hold a Mana-Shield-esque personal enchantment upon herself, but instead curses her opponent to have the opponent deal damage split between health and mana. This means that a Ventdal witch with enough mana can protect herself quite powerfully by casting Spirit Shackles on incoming threats.
The amount of damage dealt to mana instead of health is determined by:
iPercentageRedirected = piBaseEffect + ((piBaseEffect*(state+1))/100);
Current server setting piBaseEffect is 10.
Therefore a 99% Spirit Shackles will cause 20% of the victim's damage dealt to go to mana instead of health, assuming they have enough mana. Any 'overage' beyond current mana will go back toward damaging health. Ventdal's level 1 Nightgrip skill can double the effect of Spirit Shackles on monsters, causing 40% of a monster's damage to go to mana; Xaerdun's Unhallowed Runes skill can add 5-7% when cast against any target, causing up to 27% of a player or monster's damage to go to mana.