Ordered it from amazon: https://www.amazon.com/Adventure-Grid-Wizards-RPG-Team/dp/0786966211/ref=mp_s_a_1_14?crid=2IL6ZYP781QGU&keywords=dnd+battle+mat&qid=1554750814&s=gateway&sprefix=dnd+battle+&sr=8-14
If you get one use the cardboard to make yourself a screen too!
>How big is the arena?
>Grid, map, or theatre of mind?
I'll be using the full foldable adventure grid, which is pretty big (about 20x25 squares) with some terrain pieces (pillars, small changes in elevation, braziers, some hazards, and such. There will be a 3x3 platform in the middle which will serve as a sort of King of the Hill type area. I plan on having some random lair actions that occur at initiative count 20 that will seek to either encourage people to move to the central location, or otherwise mix things up. The platform in the middle will usually be safe from these. I'm thinking of things like the following:
Might also run these as legendary actions so they could happen more than once per round if I think it necessary.
> How will stealth be handled?
If a player takes the Hide action, I'd have them roll Stealth contested by everyone else's Passive Perception. Players who have a lower PP than the check "lose track of that character and don't know where he or she is until they do something that would reveal themselves (move in the open, attack, etc.). If a player sought to just hide every turn and not really participate, I'd likely leverage the hazards to encourage otherwise.
> How will general fight aviodance be handled? Druid wildshape, tiny hut, rope trick, etc?
No druids in the group, so no worries about unlimited wild shape or such. I don't plan on giving them in-game time to prepare. It's a dream, so they just appear in the arena, the Moon Deity announces the contest, and they begin! So things like Tiny Hut are a non option. Things like Rope Trick won't work, as extradimensional space cannot be created here. They've had their fair share of unexpected interactions with teleporting or creating extradimensional space in odd places, so I think they'll know to expect those tricks could have unintended risks. But in general, hazards will be used as needed to encourage participation, though I am not at all opposed to tactics outside of the usual "do damage until everyone dies" game.
> Will pc’s get a short rest or long rest during this? If not how will you balance short rest classes?
Nope, this is a single battle. Definitely something that could be negatively impacted by the "5 minute adventuring day" effect, but otherwise, I've given the short-rest classes (just our Monk, really) tools that help to combat that (an item that restores a ki point on crits/kills with unarmed strikes). Otherwise, I could do some minor random reductions to long rest resources to represent being part-way through a day and reduce crazy nova.
> What level are the pc’s?
Level 20, baby!
> How will you handle summoned creatures? Can the cleric planar ally?
The same way I usually do. They can use them as written, but attacks are rolled in batches to save time, and if you don't have your turn planned out when you get to it, they attack the closest enemy. Haven't had a problem with this, as no one wants their turns to take forever. The cleric could cast Planar Ally, but it'll take about 100 rounds of combat haha
> How about divine intervention, wish, true Polymorph, shape change, simulacrum?
There's only one player with level 9 spells (Wish being one) and I'm going to rule that it can only be used for the "duplicate a lower level spell" effect. Otherwise, run them as written, paying close attention to casting time.
> What about players teaming up?
Totally allowed, if not encouraged. Two players are very much more combat oriented than the others, so I absolutely suspect someone will propose teamwork.
> the problem I see is that one person is winning and the rest are losing full stop.
That's generally how Battle Royales work, eh? Yeah, my concern is with people sitting around for an hour or more if they get knocked out early, so I had a plan for that: when a character falls, a Shadow (or another creature I choose) rises there with the goal of taking down the person who defeated them. These creatures will be immune to damage, effectively making them active hazards. That and having them do rolls for the lair actions and such to make sure people have things to do if they fall.
So that's my thoughts. Just need to figure out if I'll let them know ahead of time that we'll be doing this or make it a surprise.