These three cards are from from APs in the Ancient Relics cycle.

* Arcane Tampering: "After a character exhausts to trigger or pay the cost of an effect, its controller must sacrifice that character."

A local player argues that this card means the controller sacrifices if:

1) The character exhausts to trigger, or;

2) The character pays the cost of an effect, with or without exhausting.

If I'm understanding it correct, and I think I am, the key is that the character exhausts , either to trigger or pay. Just need a little clarification on this one.

* Canopic Jar: Can someone give an example of how this card might be used? Its application seems very narrow, perhaps all but useless. Am I missing something? Is there a clever combo with this card?

* Premature Detonation: Even worse than Canopic Jar, I can't imagine how this expensive card is helpful to the active player. Its utility must be very narrow--perhaps to prevent a character from somehow committing to a story after the commit steps are typically over? Otherwise, it seems downright harmful to play for most any scenario that comes to mind.

You're correct re. Arcane Tampering, it's clearly worded so that the character must exhaust.

Canopic Jar has errata (page 2 of the FAQ), the second ability should be a Passive, not a Response, and read 'You may exhaust Canopic Jar and discard a card attached to it to trigger that card's ability without paying any cost'.

Not familiar with the card itself but it seems like you would use it to 'capture' a character of yours, or your opponent's, that has a useful ability on it, and then discard that character on a later to turn to get one last, free, use of their ability.

Premature Detonation at 3 Loyal Cost wouldn't get played much, but I guess you could use it along with a subsequent event or ability that needs your opponent or you to have exhausted characters? None springs to mind off hand but I'm by no means familiar with the whole card pool.

Canopic Jar may have its uses, but there's quite a consensus that 'Premature Detonation' is completely useless - or at least that noone has been able to figure out a use so far.

I'm guessing the card was (too) powerful during playtesting and then got nerfed into oblivion without revisiting it.

Only use I can see for Premature Detonation is to lay down your opponent's characters if they had "exhaust to..." abilities, and were leaving it to the last minute to use them, to prevent them from being able to do so (as Active player gets first action - which would be you, if using Premature Detonation, based on its requirements - after your opponent commits defenders).

But as your opponent's characters are all going to 'ready' in moment when it's their turn next, and yours will stay down unless you win Arcane struggles or have other tricks, then it could put you at quite a disadvantage.

Aside from that, there are very few cards take advantage of exhausted/exhausting characters. A few can commit while exhausted. The Night blanks text boxes of non-unique exhausted characters (but affects yours too). William Bain can cycle through your deck, if you can afford to pay 1 to look at the top 2 cards, for each exhausted character of your opponent's (though they probably would have exhausted sufficient characters anyway to defend stories).

Canopic Jar may have its uses ...

I'm having trouble seeing how. If I understand how it's used properly, there are few character cards that can be attached and used with it to any useful effect. I was hoping someone might have a good example or two for how it might be employed.

Well, I think the most common scenario is that your opponent destroyed one of your characters with an ability that is crucial to your deck. With Canopic Jar you'll get another shot at using it. Of course you could also capture an opponent's character with an annoying ability that you can then use for yourself, once. Point me to a deck, and I can give you examples.

Looking over the list of recently played decks, I see the following: Trial Judge, Naomi O'Bannion, Hack Journalist, Clover Club Torch Singer, Peter Clover, Lena Di Boerio, Hydra, Y'Golonac, Cthulhu, Faceless Abductor, ...

It's only one more use, but for some cards (Hack Journalist!) that's all you need.