Hi everyone,

We're a fairly new group who are currently playing Phandelver and Below: The Shattered Obelisk. My Players (Ranger, Wizard, Cleric) have never played DnD before and while i have played DnD as a player for a year and know the basics pretty well, its the first time i am a DM.

After they survived the Goblin Ambush they decided to check the Cragmaw Cave out. They were out of Spellslots due the previous encounter and the Goblin Boss basically ripped them apart all by himself. (Double Attack with 2 lucky rolls and two were down) before the first round was finished.

I let them escape with the Goblins laughing at them, of which they went back to the task to return the Wagon. Upon returning it and getting their gold, Elmina Barthen sends them off to save Gundren, which my players connected with the Cragmaw Cave, thinking its the Mine of Phandelver. (Obviously, they have not explored it and connected it to the Mine of Phandelver)
I even gave them each a healing potion for the promise to look for Gundren.

Upon returning to the Cave, fully rested and Milestone-boosted to Lv 2 (i felt this was unearned but i let them have it to give them a fighting chance, as the book mentiones that they should be lv 2 upon reaching the village), they once again got taken apart by the Sentry in front of the cave, even trough i had the Boss staying back as he threw a nat 0 in perception and thinks his little underlings are shooting at shadows.

The two goblins with 3/4 cover have 20AC and will never be hit by any traditional ranged attack, my party is wary of using their valuable few spellslots on what is basically just the preample given how much of the map they dont see yet and if they get to close combat, the goblin boss with his Multiattack and his Redirect Attack would once again remove any close combat threat.

I am already holding back as much as i can, have them act stupidly and not even use Nimble Escape or similar but it seems pointless and the Encounter Calculator here on D&DBeyond also shows it as absolutely deadly, something i can just sign myself. I do not see how this group could survive the goblin boss, let alone the rest of the Cave.

May someone give me tips how to play this (and the future) encounters or tell me what i do wrong? We kinda wasted 3 hours this session and are exactly where we started.

It sounds like they are getting hung up on the combat part of things. You could give the goblins fewer hit points. Or treat the lowest level ones as minions (only 1hp). If they get hit, they go down regardless of how much damage is done. 

You could also speed things up by giving the goblins wisdom or intelligence checks each round before their turn. If they fail, they do something stupid like move from cover to attack head on. 

It's important to remember, the way the book describes the encounter is how it should be set up upon arrival. Once you and your players are there, it's a living location that morphs with the choices taken, right? Let your monsters and NPCs make dumb choices sometimes so your players can be the heroes they're meant to be.

There's nothing wrong with telling your players that the cave isn't the mine if they're thinking there's a huge mega dungeon coming up and conserving resources to the point of not being able to fight properly. Also in addition to using the minion rules Venpal mentioned don't be afraid to adjust things on the fly once they get to the cave, you can reduce hit points, make goblins do stupid stuff and remove goblins entirely from the fight if that helps the balance. Basically until the players actually encounter something it only exists in your head and you can easily make it *not* exist. Even after combat starts don't forget that goblins are smart, and that doesn't just mean they use cover, it means that if they see three of their mates die there's a very good chance they'll run away

There is a darned good reason that Lost Mine of Phandelver came with two of the five premade characters being fighters. The premade lineup for the adventure was Rogue, Wizard, Cleric, Fighter 1, and Fighter 2. What you're seeing here is that the party are suffering from the lack of fighters. The adventure is designed for five players, and it is designed with the assumption of particular class choices. This often gets overlooked by DMs and players who then complain that the adventure is too difficult or too likely to TPK the level one characters. I've now run Lost Mine of Phandelver 7 times. I've never had a TPK, nor have I had a player character drop to 0hp before level 3. 

My point here is that to get the best of the adventure you really do need to get a few more players into your group, or give them some hirelings as were described in the original Lost Mine of Phandelver adventure. I'd also seriously recommend that you don't run this adventure, or the Phandelver and Below adventure with characters made with the 2024 ruleset. They don't work quite as well. 

Perhaps too, I'd suggest getting your ranger to switch to a fighter. Explain to the group that this adventure was designed with premade characters in mind. Show them the premade characters from the original adventure and explain that the designers assumed that characters with these classes were assumed to be embarking on the adventure. As a new DM and as new players it is often best to run with these starter chartacters. Choosing to run the adventure without these (particularly the lost mine of phandelver part) will mean a detriment to them as players. You've already seen that Cragmaw Cave is designed for melee more than range. In fact most of the locations are designed with melee in mind. So a ranged Ranger will be at a massive disadvantage both to them and to the group. Of course as a DM and as players, you didn't have the experience to know that going in. Put simply, the early sections of the adventure more or less require a melee combatant.

Many experienced DMs will write off what I've just said, but I honestly believe that for newer DMs and newer players, starter and premade characters are the way to go. The will assist you in getting the most from the adventure, as well as helping you to learn the system. D&D is often pitched as flexible and only as limited as the imagination - sadly this isn't the case. There are assumptions made when designing adventures.

TL;DR - You didn't do anything wrong. The writers of Phandelver and Below messed up by not factoring in that Lost Mine of Phandelver was built with the assumption that the party would be Rogue, Cleric, Wizard, Fighter 1 and Fighter 2. To correct for this, do check out the original Lost Mine of Phandelver information if you can get your hands on it, and recruit extra players to fill the gaps. Suggest too that Ranger becomes a melee Fighter.