This is a quick little thing I wrote up on Reddit a few days ago. The basic idea is that you’re looking to run a game with 1 DM and 1 or 2 players. Legends & Labyrinths includes a build point system which makes it very easy to build encounters for non-standard group compositions, but very small groups pose some unique challenges. It can also be useful to have some quick conversion guidelines for published adventures.
So if you’re looking to DM for a group of 2 PCs:
(1) One of the PCs should be a cleric.
(2) Give them plentiful healing resources. At 1st level, a wand of cure light wounds with 15-20 charges should do it.
(3) Take any adventure designed for 1st level characters and do the following: For any encounter involving multiple creatures, halve their hit points and reduce their number by half. For any encounter involving a single creature, reduce them to minimum hit points.
And that’s it. You’re good to go.
For example, consider the encounters found in the first dozen keyed areas of The Sunless Citadel:
Area 1: 3 dire rats (5 hp) = 1 dire rat (3 hp)
Area 3: 1 dire rat (5 hp) = 1 dire rat (2 hp)
Area 5: 3 skeletons (6 hp) = 1 skeleton (3 hp)
Area 6: 1 dire rat (6 hp) = 1 dire rat (2 hp)
Area 10: 1 quasit (9 hp) = 1 quasit (3 hp)
Area 12: 1 dragonpriest (42 hp) = 1 dragonpriest (21 hp)
The reason this works is because encounters are designed for 4 PCs: If you halve the number of PCs it means that monsters will generally live twice as long and have only half as many targets to inflict damage on. That means that the difficulty of an encounter roughly quadruples if you halve the the number of PCs. So we adjust for that by halving the monster’s hit points (so that they survive half as long) and halving their numbers (which halves the number of actions the monsters can take each turn).
Adjusting for having only one player in D&D is a little tougher because there’s no margin for error: If a PC gets knocked unconscious in normal play, they can be revived by other members of the party. If a solo PC gets knocked unconscious, it’s an immediate game over.
Here’s what I recommend: Start the PC at 3rd level and then run them through 1st level adventures that have been adjusted as per the above. (You’ll probably want to have them use a cleric again. Or find some other way to make sure they have access to magical healing.)
I have done very little one-on-one stuff, but this method seems to work.