I've solo'd Felucca champs dozens of times (Ilshenar ones are too slow and paragons are a pain). I can't imagine how the Bedlam & Twisted Weald Spawns can be Solo'd, but I can give some tips on most of the others.
Baracoon I've done plenty of times on a necro/mage & ABC Archer. Easy to move the earlier spawn with necro/mage. Just wriath form, EV, wither. For Baracoon himself, any archer or mage style with vermin or repond slayer makes easy work of him. He just stands there while you pound on him. EVs, pets & melee make him move around, which just makes stuff more difficult. My current favorite for this is Necro/Mystic/Mage. 800 total skill points, which requires some special equipment. But really, just a normal necro/mage or an ABC archer with a fast hit area bow for early spawn & repond slayer for later makes this easy. Takes about 30-40 mintues to solo.
To me, Rikktor is next easiest, I do this one several times a week on an ABC archer. I have a top-of-the-line ABC archer suit on my main shard, but it can be done with far left. I created a low cost (low PS, cheap equipment) character on a slow shard just for this purpose, and was able to solo Rikky with about 10m in equipment (cheap arties like RBC, Jackal's) and most skills in the 90s (archery to 110), and 2 imbue'd bows. One with hit area for first 2 levels, and reptile slayer for last 2 levels. The tricky part to this spawn is killing the level 3 & level 4 spawn quickly enough. For the level 3 I use enemy of one on the drakes, which allows me to take down both drakes & justicars in 2 shots (reptile slayer x-bow). If you can maintain this pace, killing everything in 2 shots, you'll be able to move the spawn solo. The trick, really, is to not get too much stuff attacking you.
If you can learn how to move, so only 2-3 things are attacking you at once, you can keep up the killing pace (take out justicars before drakes if multiple are on you). For Rikktor himself, it's just a matter of learning how to move. Consecrate lasts 4 shots, and it's simple to stay about 5-6 tiles in front of him while you fire away. When you hear the stomping that leads up to an earthquake, you can get off 2 more shots before needing to move away. Then you can move right back and fire. If you do this spawn in Destard, the northern part of the spawn is easiest, just make sure you clear it while working the level 3 & 4 spawn; and the great benefit is that there's a rez ankh right there to use if you make a mistake (can't remember the last time I had to use that at any point in the spawn).
Arachnid spawn is similar to reptile with ABC Archer. For the level 3 spawn, I enemy of one the Matriarchs. That way, you can bring down dread spiders & matriarchs with 2 shots apiece. Again, keeping a good pace is key to moving the spawn. Don't get yourself buried because if 4-5 of them mana dump on you at the same time, it can kill you (and the time it takes you to rez might cause the spawn to drop back). If you fight no more than 2-3 at a time, you can bring them down steady & move it. For the level 4 spawn, I like to enemy of one the poison eles, and rely on slayer property on the avengers. Takes about 4 shots each, which isn't optimal, but fast enough to move it.
For Mephitis herself, there's 2 challenges. First is her web attack of course. Key is to not let you HP get too low when fighting her. If I get below 80 HP, I get far enough away to let the next bandage kick in. If I've got 100+ HP, I can survive a web attack. Second biggest problem with her is that she doesn't slow down as she takes damage (Rikktor slows down A LOT). So, picking the right place to fight her in Felucca makes a big difference. I like the Ice West Area for her because of the big open space. Khaldun is good too, with the big open field to the west, or Island. I've done her at Oasis before, but it can get dicey when you lead her around the circle if she leaves webbing behind on the ground.
Just as a note, I've also solo'd Mephitis with a Provoke/Discord/Mage, but this takes some planning. When clearing out the level 3 & 4 spawn, you have to make sure you advance all of it and don't leave pockets of lower level spawn. That way, you'll have enough high level spawn leftover to use on her. A good bard will be able to bring around 10-15 Poison eles & avengers, along with some dread spiders matriarchs. You can also summon earth eles & provoke them onto her, which keeps the rest of the spawn alive & doing damage longer. You have to let the provokes do the damage, because if you attack her directly, she might web you in and it's not worth it; same with EVs. This method is actually funny as hell as you see the avengers & eles try to escape when their HP gets low, and she'll throw out a web and drag them back. This method is not as fast as with an archer, and take a bard that really knows what they are doing.
Semidar can be handled by an ABC archer in exactly the same way. Demon slayer can bring down the succubus & demons in about 3 shots, which moves things along just fine. Gargoyle's are demon slayer too. There's 2 important tricks to this spawn. First of course is to be a female. Second is selecting the location. To me, there's 2 places to fight Semidar, either Oasis or Island. At Oasis, you can trap her on the ledge to the west of the altar. Come back around, and just pound away at her; 200 points a pop with a good slayer bow and she's a sitting duck. Other place is Island, you can trap her on a ledge on the northern section of the spawn. Again, once you get her trapped she's done in a matter of minutes.
I've also done this spawn with a necro/mystic/mage (as a hinted at before with baracoon). I haven't had the opportunity to try it solo, but I've done it 2-man and I'm certain this template can work great - maybe even better than ABC archer. Best thing about this template is that you have magery spells at your disposal when trapping her. Either invis and run off, or get her on the ledge and teleport away. This template deals out massive damage, so it would be no problem moving any of the spawn with a combination of wither, hail storm, EVs, colossus.
Neira I have never tried solo. The secondary spawn would certainly be a huge challenge. Personally, I don't have quick enough fingers to cut up the bones so that's not really an option for me. When hunting her in a party I have seen dexxers trap her, so if a sampire is able to do that, I think it would work. I do have a provoke archer that I've always wanted to try on her. This char is set up with about 810 skill points, and is an ABC archer in most respects, with provoke & music. The biggest challenge, as I see it, is that rotting corpses are pretty difficult to provoke - fail a lot even at 120 especially onto a boss. So, depending on how that provoking goes, could make for a very long fight. An archer definitely has the firepower to bring Neira down, just don't know if the provoke part can hold up against all the secondary spawn. Was thinking of trying the necro/mystic/mage template as well, with wither & hailstorm to deal with secondary spawn and corpse skin & flamestrike for Neira. Maybe, I don't know.
With a Fey Slayer book, Lord Oaks is a piece of cake for my necro/mystic/mage now. Rising Colossus to tank (might have to cast a few because he dispels), then just sit there and pound away until you need to cast another. Key to doing this template is that you have to be negative karma for it to succeed. To move the fey spawn solo you have to kill everything. I don't think you can move it solo killing just wisps & centaurs. Necro is negative karma anyways so it's fine. This spawn takes a super long time to do, but the boss is not hard right now. In the past, I have solo'd Lord Oaks (the boss, not the entire spawn) with a discord tamer. If you learn how to move so you can move in and throw on a few vet bandages while avoiding his agro, it's not hard to do. His area attack is weak, but it causes him to re-target you, so you have to be ready to move & invis.
So, those are some detailed explanations for the felucca spawns - actual data from my own experience (except where noted). I don't know how to record & post video of me playing UO, but I'm not making any of it up. One other thing I'll point out is that if you're willing to consider switching characters in the middle of a spawn, a sampire or necro mage can move any of the early spawns quickly. Personally I prefer sampire for first 2 levels of reptile & arachnid; and switch to archer when it switches to level 3. Remember, you can use valor to advance one skull, which is a handy tool when you're switching so the spawn doesn't drop back. For Baracoon I like necro/mage the whole way. For Semidar I like archer the whole way. Oaks, necro/mystic/mage whole way (although, doing this spawn solo is like pulling teeth). Neira, no clue, just some guesses.
. No paragons there.
