Bloodstones: Some magic items, such as golems, normally only work for their creater. And sometimes, the creater of a magic item only wants it to be useable by one or several selected people. Bloodstones help with both of these.
When a magic item is created, the creator can craft one or more bloodstones (which usually use a crystal for the base material) at the same time. After that, a creture must bond with the bloodstone by pouring its own blood over it. This costs 1 hp times the caster level of the bloodstone. After this, the creature that bonded with the stone is considered one of legetimate users of the magic item, and no one other than a legetimate user of such a magic item can use or activate it. If several legetimate users who all have bonded with different bloodstones tied to the same item struggle for control of it (like several users trying to give orders to a golem), resolve the situation by requiring Concentration checks. The character who rolls the highest Concenctration check result can use the item or give it a command during that round.
The bond with a bloodstone can be destroyed by successfully casting dispel magic on the bloodstone versus the caster level of the bloodstone. After this, the bloodstone can bond with a new user.
While weaker enhancements usually aren't worth the added cost of a bloodstone, they are very common for the more powerful ones. They are especially prevalent with golems. Golems work on all sorts of tasks, and it simply isn't practicable to force the creator of a golem to constantly supervise it when he could do more important things (like creating more golems). On the other hand, no one wants just anyone to be able to order a golem around, since they can be devastating in the wrong hands. The bloodstones allow trusted people to control them, but if necessary, their control can be quickly taken away with a simple dispel magic. Needless to say, the bloodstones of powerful items are normally kept at very secure locations...
Moderate Divination; CL 7th; Craft Wondrous Items, locate creature; Price: caster level x 160 gp.
One-shot enhancement: It is possible to create cheap versions of enhancements that only work for a single use. One-shot weapon enhancements will work for a single attack, while one-shot armor enhancements and similar defensive items will only work against a single attack or effect - the first such attack or effect the wearer is subject to. The prerequisites for this kind of enhancement are identical to the normal version, but the basic cost is only 1/50 times the normal cost. The magical aura surrounding a one-shot enhancement is one level weaker than usual, down to a minimum of "faint".
One-shot weapon enhancements are popular with assassins and other people who need to make their first hit count. Combining this with bane enhancements is popular. One-shot armor and similar defensive enhancments (such as items that grant bonuses to saving throws) are popular with public figures and other people who have to fear assassins. It will only protect them from one attack, but that one attack is often all their attackers have. They are less useful to adventurers and other people who find themselves frequently under attack, as the enhancement doesn't discriminate between various attacks by how dangerous they are, but simply triggers at the first attack, no matter how weak it is.
How do these sound? Are they balanced?
(Crossposted to dungeon_masters)