adapting monsters from prior edition

[Torpin]

we are getting to a dark chapter of my campaign and i want to adept some creatures from the book of vile darkness from 3rd for my players to fight, particularly the vaath, any resources, suggestions or guidelines on how?

[stoutstien]

The good news is building new NPCs for 5e is pretty easy but you have to work backwards. What CR are you roughly shooting for?

[Torpin]

3-4 maybe 5, they are 6th level with some magic items too powerful for level so i want to give them 1 per pc

[MrStabby]

3-4 maybe 5, they are 6th level with some magic items too powerful for level so i want to give them 1 per pc

So CR 5 is probably about right if you want a tough fight. CR 4 would probably be something that would slow them rather than being a particular risk.

My tip is to focus on the iconic abilities and delivering something fun there. Once you get a sense of the power of those, work on the other stats. Try and preserve rankings, but absolute values can all be adjusted.

[D&D_Fan]

I think this fits the category of homebrew better.
This couldalso be usefull maybe?
https://media.wizards.com/2015/downloads/dnd/DnD_Conversions_1.0.pdf

[NaughtyTiger]

I really like how the 4e monster manual has stats for what you know about a monster based on skill checks.

i wish 5e had that.

and that an 8 in nature should say about slimes "lightning kills everything"

[Ninja_Prawn]

Yeah this thread might belong in the homebrew subforum.

I've 'converted' a fair few older edition monsters to 5e over the years (not the vaath, unfortunately; I don't own a copy of the Book of Vile Darkness). My stance on it is that you should generally rebuild them from the ground up. Occasionally you can lift a specific ability or effect whole cloth, but mostly you can't. Like Mr Stabby, I don't subscribe to any formula for converting 3e HD, AC or anything like that; I think you're better off making a judgement that captures the flavour even if it perhaps ignores the numbers.

Really, converting older monsters isn't all that different from writing totally original ones. It's a convenient source of inspiration, but you still have to do all the work on the mechanical side.