This page has helped me balance combats for a very long time. You can also refer to the Dungeon Master's Guide as it also has material to help you balance out combats for various party sizes.
level 3 - Lightning Keep - free. could easily be dialed up by choosing a higher CR dragon from the provided list.
level 4 - Prisoner 13 - free. if you're going to carefully construct a one-shot party, might as well pull a heist.
level 8-ish - Harrowhall - $ book. lots of advice provided for adjusting allies/impediments to dial in more or less challenge.
level 10 - Heroes' Feast - $ for charity. seems pretty self-contained and less obviously adjustable but i haven't read far into it.
level 16 - Giants of the Star Forge - free, iirc? optional contests of 'spirit,' 'grace,' and 'resolve' before some big fights.
level 20? - just fight Vecna, maybe - free. gee, i sure hope he doesn't summon an army of undead that takes 3-4hrs to mow down...
edit to add a few more sessions that work fine out of context of their original official adventure... * level 5 - LoX, Ch.3: Treacherous Salvage - spelljammer. explore a spooky space wreck, then some ship-to-ship combat. * level 9 - RotFM, Ch.7: Doom of Ythryn - icewind dale. random encounters and a demilich or go straight to the Chain Lightning Stadium. * level 11 - DC, Leilon Besieged - icespire peak. tired of dungeons and arenas? a huge battle made manageable by a nice flowchart. * level 12 - DC, Ebondeath's Mausoleum - icespire peak. another dungeon but then big bad makes players fight... each other!
I am thinking about trying to DM playtest characters.
I am thinking level 5 /10/15 /20.
Trying for 3-4 players.
What should I have them face at the different levels?
https://kastark.co.uk/rpgs/encounter-calculator-5th/
This page has helped me balance combats for a very long time. You can also refer to the Dungeon Master's Guide as it also has material to help you balance out combats for various party sizes.
edit to add a few more sessions that work fine out of context of their original official adventure...
* level 5 - LoX, Ch.3: Treacherous Salvage - spelljammer. explore a spooky space wreck, then some ship-to-ship combat.
* level 9 - RotFM, Ch.7: Doom of Ythryn - icewind dale. random encounters and a demilich or go straight to the Chain Lightning Stadium.
* level 11 - DC, Leilon Besieged - icespire peak. tired of dungeons and arenas? a huge battle made manageable by a nice flowchart.
* level 12 - DC, Ebondeath's Mausoleum - icespire peak. another dungeon but then big bad makes players fight... each other!
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