Hi again,

as an example for my question:
if automatic regen has to be used at the beginning of my turn,
and by doing so, I will lose a power that I want to keep, can I just not use the card? Or do I have to regenerate?

I'll re-phrase,

Of course they are optional in general, but I guess i'm wondering if there are any (maybe those that I don't have... like damage shield, that's the one sort of like mystics right?) that are automatically trigerred unless you say otherwise. Since I remember reading that mystics could harm your own chararacer if it was not cancelled.

ex: As in an EE that hits the shooter because he was adjacent to his target. In such a case, I heard that mytics would then retaliate against its possessor (or something like that).

Although damage shield probably wouldn't retaliate against EE anyways because it has to do with close combat attacks, are there any cards that are non cancellable that I am forgetting?

From the Danger Room rules:
I hope this answers your question.

There is also a small number of feats that aren't entirely optional.

If a character has Life Model Decoy, it can't be healed. You can't "turn off" the feat to use Support on him.

Likewise, ATAs can't be turned off to get the original TA back.

And Sidekick can't be turned off for carrying purposes.