D&D 5E Creating a 1-shot item that goes off with damage

[patwil]

In essence I'm trying to create a trap but one that is beneficial to the player. I'm envisioning it for my familiar and if the familiar takes damage a shield spell goes off.
Now I know something like this can't be common or everyone would have one thereby wrecking the concept of a static AC, however maybe something that takes a week or so to create and you can only have one created at a time?
So, how would someone go about making this? Or am I asking for too much cake with my character?


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[jgsugden]

It is like a contingency spell. That is a sixth level spell. The elemental gems are like a one use fifth level spell. I'd make these items the same rarity as an item... or I'd just allow contingency to work on a familiar.

 

[thethain]

You are basically wanting a spell scroll that goes off automatically, which is a bit much, but its a level one spell. If I was willing to let you create such a thing it would probably be in the neighborhood of 150~250, and require attunement, and use the reaction of the creature when activated.

Reason for the attunement is that being able to pre cast shield weeks in advance is too powerful at higher levels when the gold cost is no longer an issue. A wizard could have a dozen shield runes on him, but if it requires attunement then he would likely only have one attuned at a time (if that).

 

[patwil]

As a player, I think I like "thethain's" response, but it appears that "jgsugden" has found a RAW response, which wow - 1500 gp plus the cost of getting someone to cast it for you and only lasts 10 days? I like my familiar but that may be a bit much

Thanks for the help folks



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[thethain]

As a player, I think I like "thethain's" response, but it appears that "jgsugden" has found a RAW response, which wow - 1500 gp plus the cost of getting someone to cast it for you and only lasts 10 days? I like my familiar but that may be a bit much

Thanks for the help folks



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BTW. There is a 100% RAW version you can use that is MUCH cheaper than what he mentioned. If you find a ring of spell storing, you can cast shield on it 5 times and let your familiar attune to it. Your familiar can then cast the spell using the ring (assuming a ring remotely makes sense, such as on one claw of a bird) magical rings and armor resize to fit their owner. Whenever he uses up his shields you can recast them before a long rest to recharge the ring.

 

[jaelis]

As DM, I would simply let you cast shield on your familiar as a reaction if it is attacked (and close by).