A heart of ice.

[Kassy]

I have a new idea for a way of casting certain spells, it involves the use of an item, but the item must be recharged now and the by the blood of certain creatures, depending on what the spell is, what would i submit it as, an item?

Oh and any ideas on this would be nice...

[manfred]

It would be System.

I think we have somewhere a system working like this, powered by the blood of draconic creatures.

[Kassy]

A system?, ok then.

Pity the poor fool who had to kill all those dragons, mines relativly risk free, should have came to me.

[Kassy]

I couldn't possibly have any ideas as to casting could i?

[MoonHunter]

Casting varies too much by system usually.

Might I suggest the item must have a blood stone or a crystal that shifts from red (full charge) to clear (empty).

Might I also suggest that the item should be used in the casting as a "pointy wavy" thing so it is obvious that it is the foci of the power (and those items that are not required to do such, have less power per effect. )

The rest of the casting is per requirement of your game system/ world. This way the magic could easily fit your world.

I would write the system up given relative strength of points of blood to given effects. Thus a dragon's blood might provide 500 points of magic energy, while a rabbit mere 5. Then give that a small spell uses one points, a spell uses 5 usually, scaling spells multiples of 5, and massive spells 100. Or some such

[Kinslayer]

If it needs blood to function, that's a built-in gauge right there.  It only needs a viewing window, or a hollow center so you can listen/feel it being swished around to tell how much sanguine juice is left.  It could also have a stabbity point at the end with a hollow tip, for blood-drinking purposes.

Another thing for possible consideration is that cold is really the absence of heat.  Where does all of that heat go when you chill something?  That could be what's burning off the blood in the tube, or it could potentially build up enough to damage the wielder.