I have a question regarding the event card from PotS "He Calls It Thinking"

Can you attach the event card to a character with immunity to events such as "The Red Viper".

I would say NO, since the text that instructs the player to attach it to a Martel character is a part of the resolution of the event, but I'm not entirely sure.

The second question is, would anything be different if for example the card read:

"Then, He Calls It Thinking becomes a boon attachment that can be attached to any Martel character."

Let me answer your question with the question I typically ask when this sort of situation comes up:

If an event card said "Choose an attachment in play. Discard that attachment." could it discard an attachment from an "immune to events" character like The Red Viper? Sure, because immunity only protects the immune card form direct effects. That attachment-discarding effect works directly on the attachment (without choosing the character as a target). The character is only indirectly affected when it loses the attachment. So it is perfectly legal to use an event like this to discard an attachment from a character that is immune to events.

How, reverse all that and you get "He Calls It Thinking." The "Attach this card to a Martell character" effect is working directly on the event card (turning it into an attachment) and only indirectly on the character (who ends up with an extra attachment). Since the addition on the attachment is an indirect effect on the character, immunity does not prevent it.

So actually, there is no practical difference between the way it is written and your suggested text. There would be a difference if "He Calls It Thinking" said "Then, choose a Martell character and attach this card to it (counts as a Boon...)" In that situation, the event is choosing the Martell character as a target. Immunity prevents the card from being chosen as a target for whatever it is immune to.

Bottom line: Yes, you can attach "He Calls It Thinking" to an immune Martell character because doing so does not violate the "direct action of immunity" rules.

Thanks a lot for the quick answer ktom. Makes sense.