<p>That depends on levels, mechanical skill and perhaps other factors, I'd say.</p><p>I believe it's close to not doable (if not doable at all) to do it solo. It would be very hard to go past the first part (Rookgaard), maybe possible on Thais, very problematic on Demon Oak because of the amount of creatures, very very hard on Ferumbras because of lack of damage.</p><p>Five sometimes feels like an overkill because you can have someone just standing next to the CM diminishing their "damage" stacks, however Ferumbras Tower is rather slow already with five people, so you can risk running out of time and getting kicking.</p><p>My final answer would be <strong>4 4 players minimum and ideally 5 </strong>considering 5<strong> </strong>considering the time limit is short and performing tasks in general with less support from teammates is problematic.</p>problematic.</p><hr><p>Edit: One year goes by, and I now I've done Lord Retro a couple more times, even completed the Bosstiary entry for it.</p><p>The amount of players needed differs on whether the players you're doing the boss know the mechanics or not, and if they are mage(s) or not.</p><p>I'd say 3 players, one of them being a mage, is a comfortable setup to do the boss. It's possible to do the boss as 3 non-mages too but you'll have to have a team better prepared for the last phase of the boss.</p><p>My final answer after an year is <strong>3 people minimum, 4 or 5 people ideally</strong> if you manage to find people interested in doing this boss.</p>