I would say you can start check few poi bosses on rp lvl 200-250.
You can check massacre since you can just go to the first room on the east and make a fire/energy boomb. You can stay on the bomb for a while and you will able to see all monsters in the room where Massacre spawns.
You can also check Mr. Punish - just enter the seal and full south from the teleport stand on the energy bomb. You can also see the room where boss spawns. Ofc you need to stand there for a while.
The Handmaiden - enter the seal, use hur up and count all hands. If there is 6 it means boss is not there.
Dracola - You can trap on the north 2x Undead dragons and the rush full south. At the end use energy bombs so you will have only Demons and Liches (not always) on you. If Dracola is there it will come to you.
Countess Sorrow - one of the easiest bosses in my opinion. Use fire bombs to check it and nothing will come to you on the bomb.