Does multiple copies of the same spell (like Elemental Treaty) at the same location stack their effects?
In general yes. In fact in general everything stacks, so long as you're able to play the card in the first place. So, subject to the constraints that you can only play one card per type per character per check, and you can only play one card to determine what skill you're using.
See this recent thread for a specific example of Vic himself saying a very similar card/power does stack (and at a location specifically).
Only thing I'd say in general is read the card, because there might be a card for which stacking doesn't even make sense given the wording (can't think of one offhand though). But Elemental Treaty looks stack-tastic.
I believe in fact that Elemental Treaty will stack even if the different copies were played by the same player, since you (can) play it outside of a check, and its effect is "passive" in that you don't have to "play" the card again in any sense to get the benefit.
But I guess since activating a power on the spell is actually playing it, it works only if the two Elemental Treaty spells were played by different characters.
But I guess since activating a power on the spell is actually playing it, it works only if the two Elemental Treaty spells were played by different characters.
You are correct, but the key word there is activating. Elemental Treaty is always in effect, it is not activated. As such, making use of its damage reduction does not count as playing a spell. (A displayed card is only ever "activated" if using the power is optional -- i.e. it says "you may" on it).
Indeed skizzerz. Sorry I hadn't the exact text of the spell in front of me when making my remark.
I'm on my phone, but if you pull up the MM rules, it is not activating a power on a displayed card that plays the card, but choosing to activate a power on a displayed card. It is for this reason that benefiting from a power on a displayed card that is always in effect is not playing it,
(Also, I was offline 3 weeks, sorry for the late post.)