Let's see, last week I ran an 8 encounter adventuring day. I tend to use these types of Mission Days as the end result of a few sessions worth of Exploration Days with a primary focus on exploration and social pillars while the party decides what to do for their next Mission. Combat on Exploration days tends not to push them to their limit (unless they do something that forces the issue like attacking something far more powerful than them). Mission Days always have one or more goals that either cannot be accomplished or would make accomplishing the goals far more difficult if the party were to stop to take a long rest during it.
17th Level Party
Rogue Assassin
Battlemaster Fighter/Light Cleric
Hunter Ranger
Primary goal - A coordinated attack on an Illithid Hive in Pandemonium that has been attracting an alarming number of Illithid ships to it and is believed to be planning a major offensive against the PCs home world of Duotin. Party is a strike force meant to sneak in the "back door" get to the mother brain and kill it while the main force attacked and soaked up the bulk of the Illithid forces. Players are put under a non-detection spell prior to leaving, giving them 8 hours of cover against the mother brain.
Encounter 1 - An Elder Tempest had taken residence at the boarder of Pandemonium and Limbo, blocking the way to the back door. Get past it and into the tunnels to the hive.
Encounter 2 - Party makes it's way through the tunnels of Pandemonium. Survival checks lead to an encounter with 50 wights, cleric turns them, they continue on without wasting time backtracking. They also avoid 2 other potential encounters.
Encounter 3 - On a short rest at the back door waiting for the main force to get into position, a party of 4 adventurers (standard fighter, thief, wizard, cleric) driven insane in the tunnels of Pandemonium happens upon the party and tries to steal their stuff. Players persuade them to move along without using resources or violence. This allows them to complete their short rest and not have to save against the madness of the winds of Pandemonium.
Encounter 4 - Easy encounter with 2 Mind Flayers just inside the back door. Players set up a surprise round and waste them before they get a turn. Unknown to the party, had this fight lasted more than 1 round, an alert would have brought an additional 8 Mind Flayers to attack and made checks for sneaking around inside more difficult.
Encounter 5 - Teleportation block - Party was given a special magic item that would block all forms of teleportation in and out of the hive to prevent plane shifting out by the enemy. A failed stealth check in placing the item resulted in a fight with 2 mindwitness' and a party member almost being dropped off the edge of a 'bottomless' pit.
Encounter 6 - Sneaking through the hive. A series of checks leads to party discovering some of the secrets of the Hive that have the potential to help them later as well as the fate of a Tier 1 NPC friend who had gone missing years ago. A couple of missed checks lead to 2 quick fights with 2 and 3 mind flayers as well as an increase in patrols. Ultimately though, they make it to their objective
Encounter 7 - The mother brain. But something is off, it seems weak and listless, (4 levels of exhaustion). The party kills it easily... too easily...
Encounter 8 - The Illithilitch. An old enemy of the party, the Mind Flayer Zoltar, has been doing insane experiments here in Pandemonium, connecting himself to three other mother brains and using them to gain immense power. Basically a variant on the Illithilitch, but not undead and with some other powers changed up. He attacks the party and now we're in for a big fight. After he get's two of them locked down with mind blast, the Fighter is able to put Zoltar down, only to see him resurrected by 'consuming' a mother brain. This does release the stun lock on the rest of the party. Fight continues with party getting locked up and then saved by killing Zoltar again. Party could have attempted to disconnect the brains from Zoltar (some of the hints they got earlier) which would have reduced his 'lives'. Released Mother Brains would have attacked both Zoltar and the party. Zoltar tries to plane shift out when he is on his last life but can't due to successful Encounter 5 result, so the party is able to finish him once and for all. With Zoltar dead the rest of the Mind Flayer forces are easily routed by the main attacking group of Githzerai.
End result - 1 PC dead via Zoltar's Power Word kill (brought back by revivify), 2 more with less than 1/3 HP, Ranger with 1 1st and 1 2nd level spell remaining, Battlemaster/Cleric tapped out of spells, battle dice, action surges, indomitable and healing surge.
This was run in a single 6 hour session with perhaps an hour worth of breaks sprinkled in. Theatre of the Mind was used for all but Encounters 5, 7 and 8. Party will level up to 8 after next long rest.
