Q: When the “Guardian” effect is triggered, which unit
is wounded: the “Guardian” or the unit that would
have been destroyed?
A: The unit that would have been destroyed is wounded.
The “Guardian” is only wounded by this effect if the
“Guardian” itself was the unit that would have been
Q: Can a player use the “Guardian” effect more than
once during a combat?
A: Yes. Like the Naga and Demon, the “Guardian” effect
does not have a keyword, so the “once per card per
round” rule does not apply.
See FAQs: https://images-cdn.fantasyflightgames.com/ffg_content/Rune%2...
Regarding the Ferrox-Guardian interaction, I'm not 100% sure that this should be official ruling, but I would allow to wound instead of destroy AND to draw a card.
Interesting I have never encountered this before
(and I thought that this game could not surprise me any more)