I was in a bit of a rush this morning, but I still don't see much changing. Long story short, if you're going to stack things against the monster this much by assuming they have to double move to close, have no range attacks, pick a monster most susceptible to the spells the party has I'm going to run the monster reasonably intelligently. The troll would not stick around waiting to be fire bolted to death. It would run away long enough to heal and come back.
I did give Warren fey pact, but that's just a fear effect.
If Sarah backed away after Shocking Grasp and the Troll was frightened it should not have been able to move closer to Sarah unless Sarah and Warren totally botched their positioning. Cause Fear is one of the best 1st level control spells and if you land it in melee (not sure Warren was in melee) you should take an AOO and back away trading one AOO for 3 regular attacks.
Until it made its save against Cause Fear, the party should have had it at Range, hitting it at will.
While I think it is going to be very difficult for any characters of 1st level to down a Troll, this party demonstrated no cooperation at all. Also why is Warren using TTD instead of Chill Touch?
1. Faerie Fire is a waste in this situation IMO, you need to control its movement.
2. Sarah should have some kind of first level spell. With a 16 AC shield maybe.
3. I think either THL or Cause Fear were both good options on round 1, if you were going flee. Using both is dumb, and using THL if you are going to attack is really dumb as it puts him on the ground where you are getting disadvantage.
If you are going to fight (which is not smart), the best spells you have for this combat are Cause Fear, Dissonant Whispers, Firebolt, Chill Touch, Produce Flame, Entangle, and Tasha's hideous Laughter in that order. If your Dwarf speaks Giant add Command in there after Cause Fear. You need to leverage those spells to maximum effect.
In the situation you describe; here is how this should have played out (trying to use the same rolls you did in the first round). Iam also giving Wiz a familiar:
Round 1:
1. Barry (barry could use either VM or DM, but since he is not frightened yet we will go with VM). Troll saves
2. Troll runs up next to Sarah and Will
3. Sarah uses Shocking Grasp and backs away (troll down 2 points)
4. Warren: casts cause fear. Troll fails
5. Wiz backs away (Troll has no reaction with shocking grasp), casts firebolt and misses.
5a. Wiz Owl Familiar - Uses help/flyby to give Drew advantage
6. Drew: backs up and casts produce flame with advantage. Misses.
7. Clary: casts toll of the dead. Troll takes 6 points damage.
Round 2:
1. Barry: Casts Dissonant whispers, troll saves, takes 6 damage.
2. Troll: Regenerates all damage, no one is within reach and can't move closer. Troll dodges. Fails save on Cause Fear. Troll has 84hps
3. Sarah: Cast's Firebolt with disadvantage (misses), backs up 30 feet
4. Warren: casts Chill Touch (with disadvantage) - hits for 2 damage, backs up 30 feet
5. Wiz: casts Ray of Frost with disadvantage - misses, backs up 30 feet
5a. Wiz Owl Familiar - uses help/flyby to give Drew advantage
6. Drew: Uses Crossbow straight up (dodge+help). Misses. backs up 30 feet
7. Clary: Casts Toll the Dead. Troll Makes save. Backs up 30 feet
Round 3:
1. Barry: Casts Dissonant whispers, troll fails save, takes 11 damage, moves 30 feet. Barry also backs up 30 feet. Troll is now 70 feet from closest PC.
2. Troll: Does not Regenerate because he was hit with Chill Touch. Dodges again. Troll at 71 hps. Makes save against Cause Fear (no longer frightened).
3. Sarah: Casts Firebolt with disadvantage, misses backs up 30 feet (now 100 feet away)
4. Warren: Readies action to cast Cause Fear if Troll gets within 60 feet. (Warren 70 feet away)
5. Wiz: casts Firebolt with disadvantage - misses, backs up 30 feet (Wiz 100 feet away)
5a. Wiz Familiar - uses help/flyby to give Drew advantage
6. Drew: Casts produce flame straight up. Hits for 4 damage. Backs up (Drew 100 feet away)
7. Clary: Readies action to cast Toll the Dead if Troll gets within 60 feet.
Round 4:
1. Barry readies VM if Troll gets within 60 feet.
2. Troll does not regenerate because hit with flame. Troll dashes. It moves 10 feet and triggers all reactions. Fails save against Cause Fear (stopping movement). Fails save against TTD taking 7 damage. Fails save against VM taking 1 damage. Troll at 59 hps. DM decides since he only moved 10 feet he did not take the dash action and instead readies an action to attack the familiar if it does flyby again. Save again against Cause Fear at end of turn.
3. Sarah: Casts Firebolt hits for 5
4. Warren: Fires crossbow hits for 5, backs up 30 feet
5. Wiz: Moves up, uses crossbow misses
5a. Wiz Familiar - uses help with flyby to give Drew advantage, but gets hit and killed by the Troll from redied action
6. Drew: Moves up, uses crossbow. Misses
7. Clary: Casts Toll the Dead. Troll fails save takes 12 damage
Round 4:
1. Barry casts VM for 3
2. Troll does not regenerate because hit flame. Troll dodges. Troll at 35 hit points. Troll fails save at end of turn.
3. Sarah: Casts Firebolt misses
4. Warren: Casts Chill Touch misses
5. Wiz: casts Firebolt misses
6. Drew: Casts produce flame. Hits for 2 damage.
7. Clary: Casts Toll the Dead. Troll fails save takes 8 damage
Ok here we are 4 rounds in, the party has taken no damage, used less than half its leveled spells and the Troll is at about 30% of its hit points. The party is going to get at least 70 feet away from the troll once he makes his save against CF and then continue moving away, giving them 3 rounds before they are attacked minimum. When the Troll finally makes his save against Cause Fear he is going to get hit with Entangle and THL and this is without the Dwarf being able to use command. With the initiative order the way it is Wiz can use Ray of Frost if Warren hits with Chill Touch and kills regeneration. This will rob the Troll of 10 move giving it even more limited mobility on a hit.
At which point it runs away, if not before. The troll is not on a suicide mission. A few minutes later he hunts down the party again. On a side not just about every game I've played either bans familiars attacking, or the familiar quickly dies. The moment the troll can ready an action to attack the familiar, it's likely dead.
Limfacs: With one PC having Chill Touch and 3 more having fire cantrips, the Troll is not going to regenerate often and the party will probably eventually overwhelm it even if only doing 6 DPR or so. Also Clary, Sarah and Warren have subclass abilities and while Sorc and Cleric subclasses are mostly not particularly useful in this whiteroom, most Warlock subclasses would be very helpful even at level 1. Feylock or Undead for example would really put the Troll in a hurt locker giving the party even more control. Also we did not consider Bardic inspiration in this whiteroom.
If the party could not back up this would change it a lot, but a smart party with healing word and many more 1st level slots left is probably still going to win this combat eventually ..... probably with some dead PCs, but they will still probably win.
Next encounter the same troll attacks again but has waited a few minutes and is fully healed.
Initiative
Drew
Wiz
Sarah
Troll
Warren
Barry
Clary
Round 1. Again troll starts 50 feet away because why not give advantage to the party.
Drew: sees the troll coming back, casts entangle and is out of spells. Troll saves, Drew moves back 30 feet.
Wiz: Casts fire bolt. Misses. Moves back 30 feet.
Sarah: Casts fire bolt and does 10 damage. Moves back 30 feet.
Troll: charges in, ends next to Barry and Clary. Can regen next turn.
Warren: out of spells, uses Fey Presence to cause fear. Troll saves. Warren backs up 30 feet.
Barry: Casts dissonant whispers. Troll saves, takes 5 points of damage.
Clary: Commands troll to flee. The troll is getting lucky another 16 for 15 save. It's unaffected.
Round 2
Drew: Casts entangle again and is out of spells. Troll fails and is restrained.
Wiz: casts hideous laughter and is out of spells. Troll makes save and is unaffected
Troll: Regains 10 HP. Attack with disadvantage. Hits Sarah with a claw, Sarah is down. Troll bites Barry and does 7 points of damage
Warren: out of spells
Barry: Disengages, moves back 30 feet.
Clary: Healing word on Sarah for 7 HP
Round 3
Drew: produce flame, throws and misses
Wiz: Ray of Frost to hinder movement if troll breaks free, hits for 1 point of damage.
Sarah: stands and disengages hoping troll doesn't break free. Moves away 15 feet.
Troll: breaks free from entangle, catches up to Sarah.
Warren: shoots troll, hits for 7 points damage. Backs up. Wishes a fond farewell to Sarah.
Barry: Mocks the troll for minimal damage if it fails, backs up.
Clary: tries command again. Troll fails and has to flee on it's next turn.
However, at this point the party is out of spells and the warlock has used his fey pact. I see no way the troll doesn't simply continue to hunt them down unless they can get to safety.
My conclusion? Unless you run the troll as a mindless killing machine the party is dead. It may take a couple of encounters with the troll running away and returning
which would be the logical thing to do with a monster that regenerates. The only way this doesn't end with PCs dying until the troll is no longer hungry. At some point the spells that immobilize
will fail. When they do if the troll is sufficiently hurt it runs away and comes back in a few minutes. I don't care if they keep pummeling it with fire, they just don't have enough juice to keep it immobilized and they can't do enough damage to kill it for the handful of rounds that it can't move.
The PCs only live if you assume the troll fails saves and has a death wish.