I'm curious if anyone has played a campaign all the way to 20th level AND kept on going. What did you do? Did you just keep things at 20th or did you use house rules for some kind of Epic or Mythic play?
As a side note, how did 5E hold up at high levels?
I am currently now 17th level (yes, 9th level spells are scary for the DM).
My campaign will end at level 19.5 - however I plan to do a few things to take them to level 20+ so they get to experience level 20 play.
I am not 100% sure what I will do yet, but it will probably involve a planar force invading the realms, and involve them having to put a stop to it. I'll use RHoD as inspiration. They also have a few strongholds (a tavern, a fortress, and a mage tower) which I want to incorporate into this as well.
Maybe I'll get them to fight the CR30 Tiamat at the end, although I don't think they'll be able to win.
I will give them epic boons from the DMG and probably go a couple of levels over 20.
All of what @
Celtavian says is true.
My main point of difference is I use the DMG to create high CR monsters and NPCs since there are quite a lack of them in the MM (except for Dragons and Fiends). This makes them much more appropriately challenges for a high level group. Stock MM stuff doesn't stand up to well.
High level combat feels as dangerous and exciting as low level combat using DMG created creatures, I can still kill a high level character in 2 hits if I get lucky on the rolls.
My comments:
1. High level Characters have a lot of resources at their disposal and are able to trivialize the exploration pillar of the game. My group turned a month of underdark adventure into a few hours using
wind walk , and they are very effective at scouting using divination magic and stuff like arcane eye.
Big lake with a Kraken?
Wind walk over it. Burning city filled with an enemy army?
Wind walk over it. Tough encounter? Throw up a
wall of force then
Wind Walk out of it. Replace with Teleport, Fly, or whatever other resource your party has available.
They can also take extreme measures to protect themselves, so without "cheating", it's hard to wrest the initiative (the term - not the game mechanic) from them when running a module that doesn't cater for that.
In short, expect your players to have a much easier time retaining the initiative and dictating the pace of the adventure.
2. I echo harsh spell saves. Spells like
Hold Person become huge at higher levels (DC19) and battles become massive counter spelling fests.
3. NPC spell casters created with PHB rules don't hold up so well. ~100-150 hit points, concentration mechanics, and lack of good all day buffs means they can be killed round 1 in combat pretty easily.
4. High level combat is easy to run.
5. Bards and Rogues can get very high passive perceptions - and ability checks in general. Don't expect to rely on anything that requires a perception check to remain hidden for long.
6. If you use magic items, attunement starts to become quite a constraint at higher levels. My group now is starting to have a few interesting items gather dust because of the attunement limit.
Also an aside - magic items aren't too scary at higher levels. The Paladin player in my group has a +3 Vorpal Greatsword (recently acquired and all rolled for randomly) and it's impact on play hasn't been profound.
Likewise - The Wizard has a Staff of Power and Wand of the Warmage +3 - so a total of +5 to his attack bonus. It makes him like scorching ray a little more, and his firebolts don't usually miss, but I wouldn't say its game breaking.