There's been some confusion over at agotcards.org on how these effects play out:
The Last River
Challenges: Kneel The Last River to give each participating character without a <military> icon -1 STR until the end of the challenge.
Would this affect characters that become participating characters after the event has been played?
And a similar question:
Dragon Support
Challenges: Choose a participating character you control. Until the end of the challenge, that character gains melee. Then, each participating character controlled by an opponent gets -1 STR until the end of the phase.
I was pretty sure the effects create a lasting effect "on" the character participating at the moment the event resolves, so that future participating characters will not be affected, but people have confused me with various statements and I need clarification.