Jarrith is surprised to see that they are too late to get into position. He curses to himself, thinking they spent too much time back in town. This will be much, much more difficult. He silently channels some of his spell power into himself and the air around him becomes quieter. (Lose Sanctuary spell to add +4 to Hide/Move Silent checks for 3 minutes)
He then moves back around the ruins to return to the party down the hill. Once he arrives, he gives them the bad news.
"We're too late. I saw three witches already up there preparing things... they drew out a large star on the grounds with chalk or something. The Green Lady is not there yet, so I'm leery about attacking until she arrives. The only problem is that there's no way to get you all into place without being heard or seen."
He glances back up the hill, then nods to them. "Let's get the horses off the path... who knows if any others will be coming up this way to join them. Time-wise, it'd probably be faster for you all to run up the hill here rather than try and make your way through the underbrush... and three of you can portal in via Marot. How about I return to the ruins, stay out of sight... maybe even try and erase part of the star... and once the Green Lady arrives I'll yell out a signal for you to all come up. That work for all of you?"
If everyone okays this plan, Jarrith will sneak back up to the ruins and position himself right where he was before... losing his Hide From Undead spell to use Sacred Stealth again. Once he arrives, he will wait for the Green Lady to arrive. When she does and it appears as though they are beginning to prepare the start of their ceremony, Jarrith will sneak up behind the closest person and Sneak Attack them... losing a Deific Vengeance spell to channel a Razing Strike (+2 to hit, +5d6 in Razing and Sneak Attack damage) He will shout out when he attacks, so to make sure the others in the party can hear his signal that the fight has begun.
He will then dart back outside the ruins to Hide, thereby giving the others a chance to advance up the hill to join melee.