By now my avatar can kill the first little bosses. Reaper, Trolls (like the twins) and Xavara the fire element are no longer a problem now. All the bigger bosses I find now are still too strong for me. So Dragon, Ghost Corpion, Phoenix, Vrul and the Aether stuff. Does anyone have a hint what I solo can try next?
Torc the Troll in Ravenmoor and the Elder Wyrm in Boreas Colossus (gives a negative virtue hit) might be worth a shot. That was my progression route. You can dance with Trolls and Dragons and avoid a lot of hits, just needs some practice.
I'd like to see a piles of more lower, mid and near high level bosses myself. I just recently took out Xavara myself, the Twins are no big deal too. I haven't met any Reapers yet... Probably should seek them out next. I have had minor troubles with the Obsidian Giant Corpion, but... that was a few months ago, I'd probably have less of an issue now.