Iris "deathwish" DOES NOT activate when the card is attacked by Peter Saar Gwynleve.
If this is not a bug then add some tip on the "weaken" ability so it's obvious it doesn't activate "deathwish" abilities.
It's not a bug. Whenever a unit is weakened so that it's base strength drops below 1, the particular unit gets banished. A banished unit is removed from the match, it doesn't enter the graveyard and it doesn't trigger any deathwish abilities. A similar effect can be attained using Mardrome.
I understand that this has already been confirmed as not being a bug. I would just like to add a few things and maybe make a suggestion to the game itself. (I'm new to the forums and can't really make a new thread.)
So just to confirm, "Weaken" is basically a counter play to deathwish, in this post, a counter play to Iris. The game defines "Deathwish" as an ability triggered when the card is "moved from the Board to the Graveyard." Since Weakening doesn't actually send Iris to the Graveyard, her Deathwish ability isn't triggered. Also, any unit (or card for that matter) cannot exist or stay on the board if it has zero (0) Power, hence they get banished or removed from the game (same as Doomed cards).
Now, I would like to suggest making a "Banished" section for the game, where you can find all of the Doomed and zero Power cards. Not really to function as a new game mechanic but simply as a way to monitor and count cards. I sometimes forget to count the number of Priestess of Freya cards I've used which sometimes causes bad decisions when using First Light or choosing to mulligan a card. What are your thoughts?