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We had our character creation night for the work one-shot. I decided to take a lesson from what you experienced and, rather than go back into the character sheets, I had pre-gens set up so we could go into an encounter right away. Three of the players had started PCs enough they could use them and three others used pre-gens. I had set up an encounter with a map of a road leading into the edge of a light woods. The party had been tasked to track down a small band of bandits who had murdered a local baron in order to steal a dangerous artifact. I had them start after having followed the bandits' trail for over four hours as dusk began to turn to night. I then told them about a few things someone might do in that situation and had them all give me three checks: A stealth check to be quiet as they searched, a survival check to be able to follow the tracks of the bandits, and a perception check to look and listen. I used it to explain how ability scores affected skills, how proficiency worked, how expertise worked.
Then I explained how the stealth check is a contested challenge where their stealth is compared to other creature's perception. I explained passive perception (radar that is always on) and that the bad guys have passive perception, too, so if they don't say they are being sneaky I assume they aren't. I also explained how I do group checks for averages such as group stealth so one bad roll doesn't ruin it for everyone else.
This helped set up explaining difficulty challenge levels where the skill check is against a DC set by the DM based on how difficult something might be. Tracking fresh tracks on dirt has a set DC in the DMG of 15, and it helped make it clear how that worked differently from a contest.
Finally the perception check was something I explained could be either a contest or a DC. If someone is trying to stealth, then the perception check result would need to equal or exceed the other person's stealth, etc., etc. But it could also be against a DC set by the DM to hear or see something that its possible to miss which isn't actively trying to be stealthy. Basic stuff people who haven't played D&D don't know but is fundamental.
They responded really well and I'm planning on using that if I ever do this for new players again.
I then told them the people with the high survival rolls of 15 or higher were able to avoid losing the tracks, and the bard who beat it by over 5 was also able to tell they had passed by within the last half hour so they were close. With their group stealth they were able to advance unnoticed when they heard the sounds of people talking in normal voices in an area they couldn't see up over a 10-ft ridge to the right of where the road climbed up the slope. I then told them this is a good time to ask if they can do things and offered suggestions. They picked up on it well and I gave them a few more skill checks with results. They discovered the four bandits around a fire with the apparent leader holding a dark wooden box. He had opened it and one of the other bandits was expressing their concern about only being told to retrieve it. The leader told him to shut up and that he was just wanting to know what it was they were carrying was all, but started to read the parchment with some interest. I explained my personal approach to this kind of thing is to describe things and then pause. If they want to do something its a good idea to recognize those pauses and ask questions/act. But if they don't want to do anything or wait too long I'll take it as a cue I should move the story.
I also used this to explain how bright light, dim light, and darkness work in D&D, and how darkvision works since it was relevant. I drew out 20 feet around the fire to represent the area of bright light, another ring at 40 feet from the fire for the edge of dim light, and explained the rest would be darkness so those with darkvision would be limited to 60 feet of vision outside of the rings of light.
So we then talked through things they might want to do, and I explained how they would work. One new player asked about building a ladder to climb the ridge? I suggested that they could do that, and that it would require them either having the items needed or giving me a survival check to scavenge the wood to do so. I also suggested it would be a high DC to build a ladder quietly. And also how climbing the rocky but sloped embankment would work. (Strength Athletics, DC 8). They caught the hint and chose to scout around the edge of a shrub hedge. The person playing a tabaxi rogue snuck around and climbed a tree. The halfling rogue (lots of rogues) snaked up the slope quietly and easily, and hid in the bushes. The Tortle wizard and bard snuck up to the hedge to listen.
As they were all doing this, the bandits had a small argument about what the leader was doing. I had planned that the leader would then command the most vocal objector to hold the box if he was so concerned. But it would be a ploy as he had read the parchment and it included an incantation that would rend the soul out of the body of anyone holding the Orphic Shard when it was pronounced, turning them into a shadow under the command of whomever read the incantation. The idea was to make what started out as a fight with four bandits turn into a fight with three bandits and a shadow. Much tougher fight. But the tortle accidentally prevented this by failing to climb the embankment and having a low stealth check that even a bandit passive of 10 could hear. Hearing the rock slide he caused, the bandits got serious and started to investigate. Cue the artificer who cast entangle and trapped three of the four right away. The halfling rogue had readied her action to throw a dagger at a bandit that wasn't entangled and almost killed the only one not trapped. He shot a wild arrow in her direction, missing badly, before attempting to run away but getting sniped by the tabaxi rogue in the tree. The bard snuck up and cast Tasha's Hideous Laugh on the leader who had the box and was already entangled in vines. Then she slipped back into the hedge and hid. The Tortle wizard managed to climb up the embankment and hit one of the entanged bandits with ice knife which splashed two others as well. The party finished off the two bandits as the bard took the box away from the disabled leader who couldn't stop laughing at the cosmic joke that was the end of his life. Which the tabaxi rogue brought about ruthlessly by shooting him in the throat. I have murderous party for sure.

The tortle wizard took the box and was able to use his knowledge of the arcane (arcana check) to determine the language on the box was abyssal while the parchment could be read. He passed his wisdom save to avoid the Orphic Shard influencing him to use it but the player wants to keep it because that is the kind of party they are going to be. I told him sure and will make up a magic item for DnDBeyond to add to his sheet.
I then spilled the beans about how they had interrupted the leader being able to summon a shadow, and how the game is meant to be responsive to their choices like that. They liked that as it felt like as much of a reward as any of the loot taken off the bodies. Yep, looting bodies already. Brings a tear to the ol' eye.
They said it was very helpful. Those who still had characters to finish said they felt much more able to finish building or modifying their builds. All around I think it was a big success.