This question uses the first encounter of LMOP as (what I thought was) a fun framing device for an optimization question. Four downvotes in one minute makes me question that decision.
Tone is hard to convey in text, so I’ll make it explicit: this is just a fun optimization problem, not an attempt to ruin anyone’s game.
For a lot of players, Lost Mine of Phandelver from the D&D Starter Set was their first 5e adventure. The first encounter from that adventure is rather swingy, like many level 1 combats. PCs may end up victorious without a scratch, or unconscious without getting a turn.
What if you were really unlucky, though? Really, really unlucky. Can a single character unfailingly beat the encounter, despite all the dice being against them? What is the lowest level that you could pull this off?
Whatever can go wrong for the PC, will go wrong. In general, this means that they will roll a 1 on all dice rolls (attacks, saving throws, ability checks, damage, etc.) If a low roll is beneficial to them (Divine Intervention, for example), then that roll may be a higher roll.
Whatever can go right for the enemies, will go right. In general, this means that they will roll the maximum value on all dice rolls. If a high roll is harmful to them, then that roll may be a lower roll.
Four goblins. Two will use a scimitar and shield, and two will use shortbows. They use the average value for hit points.
- When combat begins, the enemies are exactly 30 feet away from the PC. Any PC-controlled creatures start as close to the PC as possible. All participants start on the ground.
- Two of the enemies (one melee and one ranged) are on each side of the road.
- The enemies have a chance to gain surprise. There is sufficient cover to try to hide on both sides of the road.
- The two melee enemies will close in. If it becomes clear that they can’t get into range, they may use an Action to doff their shields and switch to bows.
- Ranged enemies will try to stay within 80 feet (the normal range of their weapons).
- The PC has beat the encounter if they are alive when combat ends and all of the enemies are dead.
- LMOP takes place in the Forgotten Realms, so I’m going to limit sources to FR-specific and setting-agnostic official hardcover books: Player’s Handbook, Monster Manual, Dungeon Master’s Guide, Sword Coast Adventurer’s Guide, Volo’s Guide to Monsters, Xanathar’s Guide to Everything, and Mordenkainen’s Tome of Foes.
- Customizing ability scores, variant human, multiclassing, feats, and playing on a grid are allowed. All other variant rules are not.
- No magic items or magic item-like things granted by the DM (boons, blessings, charms, etc.)
- Spells/abilities you use before combat may only target you or creatures you control. Only spells/abilities whose effects last 8 hours or longer will still be active when combat starts. You do not get a rest between using any spells/abilities and combat starting.