The High Aldwin
I think the default is 4-5 actually, but I could be mistaken.I think we should stick with 4, which I believe is still the default party assumption for CR calculations (I believe).
Since this is his lair, I think it might up his CR. IIRC a normal Lich increases from CR 21 to CR 22 while in his lair.Unless Vecna gets some help.
Yes, I am putting a LOT of thought/work into this to run it as an encounter and not just a fight.
In that spirit, I will be including descriptions of what PCs experience as if narrating this to live players and I will ask for each player's choice of what their PC is doing, etc. until Initiative is actually rolled.
Players will also have the chance announce preparations (like pre-cast spells, etc.).