This ritual takes only a single day but must be performed during the three days of the full moon. The ritualist takes a steel amulet formed in the shape of a shield, suspended from a chain made of links taken from a suit of chainmail, and bathes it in his blood, being sure to anoint each of the links of the chain.
This creates a moderately powerful, and potentially life-saving, talisman. Until the next full moon, the wearer of this amulet can cast a Shield spell as needed. This spell behaves normally, lasting 2d6 hours unless expended earlier to interrupt an attack or negate a Magic Missile spell.
The Talisman of the Tarnished Shield has a greater power: if the wearer would be reduced to 0 hit points by an attack the Shield spell can counter, the Talisman of the Tarnished Shield will automatically trigger, counter the attack, and be entirely discharged, unable to be used until it is charged again.
If the Talisman of the Tarnished Shield is activated, either deliberately or automatically, the normal Dark & Dangerous Magic check must be made as usual.
Should the Talisman of the Tarnished Shield be polished, removing the tarnish from its surface, the transient enchantment will be similarly removed (and the ritualist can regain the Constitution spent in the ritual). This does not require a Dark & Dangerous Magic check.
At the time of writing, the Low Fantasy Gaming – Deluxe Edition Kickstarter is still going strong. It is more than more than 500% funded (11,068 AUD/2,200 AUD), with 20 days remaining.