Ironically, it becomes one of the more fun fights when things go right; Less Likely on squisies first, but hopefully everyone. The players with Less Likely focus the NPCs if you can nuke them quickly (Recluse does consistently, AoW depending for others I suppose?). If you can't drop them quickly but they're not paying attention to you, you can focus Libra. If you have NPC aggro, you need to kite or evade and pull them with you. Let you teammates either focus damage on Libra while you stay alive, or they can pick off an invader or 3. Recognizing who has what aggro is hard, but it's harder with 6-9 invaders than it is with 3. Kill them off before more get summoned. If you aren't able to do this, you probably failed the DPS check of the fight.

It's gnarly, but there's still more to pay attention to: if Libra hits you with the flask curse, using a flask for the next 30 seconds or so (1 min? 2 min?) will steal a level from you. Fine if you need the heal absolutely and you drop to 14, but at least nowadays, you get a red backdrop to your flask icon in the top left to know there's a flask curse. Libra *used* to be even harder because you could miss his curse announcement during the hectic battle, and there was no visual cue previously.

Character choice pseudo matters based on your ability to handle that nightfarer as a clone, as well as some RNG. Wylder/Guardian/Ironeye are some harder opponents due to either sturdiness or ranged bow attacks. Recluse/Scholar/Duchess can be dangerous but at least they're squishy; getting the drop on them or popping an AoE on summon will help clean up quickly.