I think this Halloween Event TFO is easiest solo, because an uneducated teammate – or troll – can really halt progress. Here is a video of a 13 minute, 20 second run. I did not try to get the cats, but I think I hit all the candles (the summary screen didn’t show up at the end):
For the first section, the skeletons are normally immune and can only be killed after passing through the candle light. After they walk through the candle light, the become vulnerable to attack. My strategy is to use my Plasma Wide Beam Rifle because of it’s epic AE secondary. The skeletons hit hard, so keep moving and don’t let them all hit you at once.
The next part with the Skeleton Lord works the same way, but he has a ton of HP and he will occasionally blow out the candles. Keep re-lighting the candles, and dispatch of him and his lackeys.
The Library event appears to be skipped entirely when run solo. This might prevent finding all the cats?
For the Hags, because you are the only player you will be turned into a cat constantly. You will only get a few seconds of attack time between being turned into a cat. You need to take out the skull before the Hags become vulnerable.
A Stealth Module helps a lot here, giving you time to prep between being transformed. I used a very strong alpha strike: buffed up to the hilt, and set my Agony Generator down so that it would take out the skull first, then all the witches.
For the final fight, you need to kill the Devidian Lord and his minions. He will become immune after you have taken off about 30% of his health, and he will phase you into Devidian space (or whatever). You should activate one of the 3 switches that are only visible while you are phased and continue chipping away at the boss.
After repeating the immune/phase/switch cycle two more times, the boss will fall and you will be victorious!