None that I'm aware of. I've run a quite a bit of 3.5E converted to 5E and 5E converted to 3.5E and if you want to do it I recommend you look up the respective monster in the appropriate rulebook and then scale it according to the desired difficulty (if required). For NPCs you have to do those by hand Now, that said, you can actually do a "simple" conversion using this formula (or table) for things like DCs / AC etc. It all depends on the level of accuracy you want: 5E DC = ((3.5E DC-10) /2) + 5 3.5E DC 5E DC 50 36 45 32 40 28 35 24 30 21 25 18 20 15 15 12 10 8 5 5 Finally, you might be able to find some online conversions.
