New Underdark(ish) Campaign

[Alassandra]

So I am putting together a new adventure for my players to start in January. It will be Colosseum themed with Sparticus like progression and escape. I plan on placing it in the Upperdark and run by drow having a good old time kidnapping travelers from Toril and forcing them to fight. Only hitch is I have never done any DMing with an Underdark campaign so I was wondering if anyone has any hints, suggestions, etc to help me make the game more entertaining and well planned? Any advice would be greatly appreciated. :)

[Falcon X]

Any specific questions you have?
- like, are you looking for how to survive down there, Beasts, monsters, potential bosses, cool locations, interesting finds, etc.?
- Can you tell us what you want it to look like post-rebellion, or other things you would like to see happen?


General advice:
First off, you would do well to buy Out of the Abyss. It details many Underdark locations around the Sword Coast, gives Monster encounter tables that are (somewhat) level appropriate, talks about fungi that are down there, and gives maps!
(3.5 Edition Drow of the Underdark and Forgotten Realms Underdark are also nice books to have)
(The R.A Salvatore novels Homeland and Exile are great for getting a feel for the Underdark and the Drow)

As for the setting:
Never forget that the Underdark is a living, breathing place (not literally, mostly) every bit as varied and changing as the topside. The terrain will be varied and you will find remnants of creatures everywhere.
- personal message me if you want my travelogues where I describe the terrain my players go through on a day-by day basis.

Be aware of:
Faerzress: magical substance that pops up here and there. Is bright and can mess up some spells (teleportation and scrying namely. Menzoberranzen is full of it just for that purpose)
Earth Nodes: invisible pockets of earth power hidden around the Underdark. Spellcasters trained in Node Magic (not a 5e concept) can teleport between nodes, hide stuff in them, and seal them from other casters. Great for NPC villains.
Mushrooms: everything here is made of them, just like we use plants and trees on the topside.

Tips for fun:
- Survival: foraging for food and water can be interesting for a while, but eventually gets annoying. I’d say that after the character’s seem to be getting the hang of it, just say that they always succeed.
Better: give them tools. A decanter of endless water, or an ooze that holds massive amounts of water like a sponge will fix their water problems.
A staff that sprouts goodberries would take care of food, and a musical instrument that casts Animal Friendship will take care of all encounters with mundane Beasts.
- Deadliness: Teach them early on to pick their battles. The Underdark WILL contain things hat are level inappropriate.
In my game, my Lvl 2 players were fighting some Orogs when a Beholder rounds the corner and vaporizes one Orog and charms another. My players ran very quickly around the corner and sprinted for a half hour after that. They got the hint.
- Goodness: Have them find not-awful things down there.
Maybe they befriend a flumph
Maybe they run into a town full of of top-siders living with svirfneblin and peches in a harmonious, hard to find place. The place should be full of food, music, and merriment.
Maybe they run into a Mycanoid colony.
Maybe they are invited to attend a Lou-toa wedding
Maybe everything down here is just so visually wonderous that it is hard not to love.

[Cwyll]

Have a look at things like the 'ruins of undermountain 2' box set if possible; a few interesting underground areas there (such as the forest where priests of malar go hunting 'prey'). There's lot to 'liberate' from old adventures or box-sets (night below) that delve underground. Google underdark and undermountain adventures, and you'll have plenty of bits and pieces; just make sure you let them see that it's a whole world down there, and not just tunnels and tombs.

[Alassandra]

@Falcon X:
Basically they are kidnapped topside and brought to the fighting pits where most of the game will take place. My husband had mentioned something about needing darkvision, but I couldn't find a reference. Most of the underdark encounters will be races and creatures they fight in there as well as any random things like that faerzress you mentioned which may pop up randomly. At some point they will escape (hopefully) and have to traverse the local upperdark and hide/fend for themselves until they return to get revenge on the masters. Thank you for the book references, I will get them asap.