As I said before Tin claims the Zanjir and thus they are pretty mad at Yllendthyr right now and probably contemplating war. Avalia is their mortal enemy (and vice-versa, Avalia and Tin hate each other) and the PRK isn't Tin's favorite place. So they hate all of you, and you all happen to be having a little party together. They would benefit from any damage done to these three nations.

If the leaders gave a speech or something there might be an assassination attempt, but I was thinking more along the lines of Tin being sour and wanting to ruin the festival.  Rather than an assassination, I was thinking of a bombing or shooting that only killed civilians and disrupted the event. Of course, Tin would deny any involvement.

As in for whether Tin could do this, of course they could. Considering that Avalia is right next to Tin and the two have been enemies for centuries, it stands to reason that Tin would have at least one or two spies that successfully infiltrated Avalia. They would just have to go to the festival as citizens and then plant explosives or something.

The purpose IC from Tin's perspective would be a (probably unsuccessful) attempt to scare the three nations and disrupt any talks. Tin tries to bully other countries like that when all else fails or they don't have another way to get what they want.

The purpose OOC would be to escalate tensions with the Zanjir conflict. Tin's denial of having anything to do with the bombing means there probably wouldn't be a war, but everybody would suspect Tin and suddenly there would be a lot more paranoia that the PRK could exploit.

Once again, we don't have to do this unless the people involved want to.