Bosskill give many Disc.Points
Get the Powerstone give more Maxlvl
So killing all Bosses(Hydra, Dragon, Whale) give nearly +3 Max lvl
8 Powerstones +8 Max lvl (far as i know)
Killing the Ghostship for the 9 Powerstone. I think atm is the Ghostship very hard to kill. Maybe special Galleon with 80 Cannon´s at one Side. Or two Galleon´s of this kind.
How to find Points https://atlas.gamepedia.com/Discoveries
Power Stones https://atlas.gamepedia.com/Power_Stone