When exactly does a tactic hit the discard pile? The only case I have found so far where it is an issue is with Mortella.

Simple example - Your opponent plays Seduced by Darkness (and currently has no other copies if it in their discard pile) and targets Mortella. Can I use Mortella's Action as a response and play THAT Seduced by Darkness?

More complicated example - I play a Tactic and my opponent plays High Elf's Disdain to cancel it. Can I use Mortella's ability to use the SAME High Elf's Disdain card to cancel itself? (Assuming I had two resources remaining and thus allowing my initial tactic to resolve).

Simple Example would work like this:

Seduced is played, you react by corrupting Mortella. Mortella is resolved first and you can pick a card out of the discard pile, Seduced won't be there because it hasn't resolved yet, but you would be able to at least use her ability, pick a card from the discard pile and then Seduced corrupts an the already corrupted unit Mortella.

The answer to your 2nd example is basically no. A tactic card must be resolved before it can enter the discard pile, so the Disdain would have to stop a tactic and then be put into the discard pile. You could use Mortella to use Disdain, but you wouldn't be able to stop a tactic that has already been resolved.

That is certainly a common interpretation of the process but no where is it explicitly stated when the tactic hits the discard pile. Some might argue that placing the card in the discard pile is part of the "cost" of playing the tactic. They clearly defined the zones of play in the FAQ but nowhere do they describe where the tactic card actually is while it is resolving. Is it still considered in you hand until it resolves? That seems a bit strange. Does it go to the discard pile as part of paying the cost? Or does it reside in some bizzare and yet to be described quantum state?

Looks like I'll have to submit a question to FFG ...

Pg 6 of the Rulebook describing tactic cards:

"A tactic card is normally played from a players hand, its text effects are resolved, and it is placed in its owner's discard pile"

Figures I would have missed something that obvious. Read that **** thing a dozen times...

Happy to help, I've made mistakes with this game as well, that is why this forum is so helpful.