Out of Character: the way I personally handle tactical stealthy creatures in combat, especially if they're going to be using the same tactic basically every round, is this:
Anytime the creature attacks it is no longer hidden and thus able to be directly targeted until it becomes hidden again which is determined by a stealth roll vs all PCs passive perception. If any one character beats the creatures stealth, it is not hidden as the character can essentially point the creature out to their allies. Otherwise, PCs can attempt to attack the last know location of the creature giving them disadvantage on the attack roll or ready an attack for when the creature reappears.
I wouldn't say it's too difficult, I mean these are intelligent creatures after all and would use the terrain to their advantage the best they could. Different types of enemies call for different tactics, that's all.
Zinna looks at Lorilys. " Stand up Lorilys. You are defeated already if you are defeated in your mind. We will go free." She gets to cover as well while motioning Oomigig to do the same. The redhead looks at the others. " You can go now if you like. I will not subject anyone to the tree. If need be I will run and they will surely follow me. " She looks up towards where Adsila's voice came from and calls out loudly. "May you rot along with your brethren we have already killed. I won't rest until every last one if you is dead. Make no mistake Adsila. You creature of the Destroyer, today you die. " She begins whispering, willing the words to reach Adsila.
Specific Action: She casts dissonant whispers at Adsila.
Out of Character: : I could handle it by having one roll for each side rather than each individual involved making a roll. So the elves will roll their highest modifier for stealth while the party will roll their highest modifier for perception each round. Rather than having them completely hidden I can say that if the stealth roll is higher than the perception roll any attacks or actions that require a check against the elves would be made at disadvantage. If the perception roll is higher than the stealth roll for that round all attacks and actions against the elves are made normally. On the other hand this would have to apply to Corren whenever he is trying to utilize stealth in combat when he attacks, disengages and then uses a hide bonus action; he would still be open to attack but it would be at disadvantage if his stealth roll was higher. Still, the enemy would only get one roll (The highest perception modifier) rather than each combatant making a roll every round. This would only apply to combat situations, in non-combat situations a successful stealth roll would mean that Corren is not detected.
Out of Character: : I think that sounds fair, and it will greatly reduce the number of rolls needed by anyone person. I am fairly sure Carrick has the highest Perception so should we just use his roll for the first round? Even though Zinna and Mradric rolled higher…
Edited: PaulNelson on 23rd Jan, 2017 - 7:14pm
Out of Character: : No one managed to roll high enough to beat their stealth rolls the first round, but from here out if I could have Carrick make several perception rolls to cover the next few rounds; once I have these rolls I can advise whether rolls need to be made with disadvantage or not each round.
Carrick runs to the closest tree and leans into it, still scanning the canopy. Then nocks an arrow and waits for one of the elves to make a move or speak as to allow the dwarf to home in on his target.
Out of Character: Carrick will ready an attack with the trigger being an elf makes its location (Or general area) known by attacking. I'll roll two attacks one with disadvantage for if Carrick is only shooting the general area where he believes the target to be.
-edit- oh and I will roll some perception checks for following rounds as well.
Edited: Brandonfett on 24th Jan, 2017 - 2:26am
Mradoric moves to the closest tree and tries to see any of the elves. Knowing they are good and staying hidden he knows it will be difficult to spot them. He just hopes that one shows itself to where he can maybe attack them back.