These are my picks of the Lego sets currently available in stores that will be most useful for running a fantasy role-playing game. I tend to recommend sets that are flexible and cost-effective.
New Lego GMs
Treehouse and/or Mountain Hut:
Both of these are solid choices that produce a good
variety of adventure settings. Each one has instructions to be rebuilt
into three things, and once you have experience building these from the
instructions, you should be confident in your ability to make similar
things from a pile of loose bricks.
Every D&D game needs a big red dragon, and you can have a very good
one for $15. If your party is not ready to handle a dragon, they can
take down a giant snake or a giant scorpion instead. I actually prefer
the scorpion to show off the potential of Lego RPG fights: the claws can
pick up the characters they have grappled, the characters can hack
off legs, claws, and other body parts, and they can can climb on the
back of the monster to avoid its claws (or even climb up the tail to
chop off the stinger).
Lava Falls and Jungle Trap:
Both of these sets are excellent values, almost perfect for a Lego GM.
For only $7 or $8, you get two minifigs, a good terrain feature, and a
magic weapon to claim as loot. Given that you expect to pay $3 or $4 for
a minifig, the terrain is basically free.
If you bought everything listed above, it would cost $100. As described in the Starter Guide,
the basic supplies will cost another $100. That $200 will give you
enough to run games for a long time. You will have eight adventure
locations just from following the instructions, not counting all the
terrain features that come in the Fantasy minifigures set. You will have
twelve large monsters (and three small ones) just from following the
instructions, and two or three more if you download and use the combined mixel instructions. And if you start
rebuilding things and using your creativity to create new locations and creatures, the
possibilities expand dramatically.
Expanding the Collection
can be addictive. Even though you only need a few of them, it is often
tempting to keep buying more. Right now is almost the perfect time to be
a Lego GM, because there are so many good sets available. There are so
many obvious choices, like the Hobbit sets and the new Pirate
sets, and many less obvious ones, like certain sets from City and Ultra
Agents. You are limited only by your budget and the direction you
choose to take your campaign in. I will highlight several sets, in
roughly descending order of how much I recommend them, that I find to be
good values or unexpected choices. They key to making a good Lego GM
collection is to gather up a big variety of things, because that expands
the possibilities of the people you can represent and the places you
Chima Tribe Packs, for example the the Crocodile Tribe Pack. Any fantasy campaign
needs bestial humanoids, and these also add useful accessories and pieces that will make larger monsters.
If you want to add a pirate-themed adventure to your campaign, this
will do the job nicely for only $20. You get three people, including an
excellent pirate lady, as well as a boat, alligator, chest full of loot,
and an adventure location with several good terrain features.
If you are running a game with magitech, this is a nice addition. For
only $10, you get two minifigs and a nice three-legged iron golem. A lot
of the pieces here, like the metal spiders and the translucent blue
shield, will be useful in a lot of situations.
Mirkwood Elf Army:
In general, I prefer to avoid the branded product lines. You are
getting less Lego for your money. But this set is a good deal: for $30, gives you six
minifigs, a riding wolf, and a good adventure location.
Protector of Stone: Bionicle sets are often very nice for giving you giants and other huge creatures to fight.
Naida's Epic Adventure Ship:
This thing has an otherworldly beauty that is fantastic in all senses
of the word. If you want the party to interact with fae or elves, and
emphasize their distinctiveness, this set and the other Lego Elves sets
will do that.
Swamp Police Starter Set and/or Demolition Starter Set:
Any set that gives you four minifigs for $10 is worth looking at,
especially if those minifigs have interesting features that give you and
your players new options for character creation. All the other stuff
should be considered a free bonus. You can decide whether your playgroup
will appreciate a Lego toilet showing up in the dungeon.
Senate Commando Troopers:
Star Wars stuff can often be made to work in a fantasy world. These
blue guys look more like greek-fantasy armored hoplites than sci-fi
Large Creative Brick Box:
This is the best option now, among new sets, for the basic supplies to
make a wide variety of towns, adventure sites, and creatures, and if you
are new to Lego building then the idea book in the set will help you
get started. Unlike the medium box, it is not loaded up with wheels that
are almost worthless to a fantasy GM, and it has several useful
architectural elements. The reason it is ranked so low is that it has
too many colors to be useful for building large realistic towns and
dungeons. If you want to do that, without buying a used collection, you
are better off buying more Mountain Huts or getting the larger sets from the Hobbit and Ninjago product lines. Unfortunately, there are no actual Castle sets in the current lineup. Hopefully that changes soon.