Just encountered the high level baselisk not far from Novigrad. Tried it once, died in one shot, reloaded to a save just before I tried, and it aggroed again. Figured I would run since most mobs have a very short leash from their camps. Not this. It shrieked and kept following me. Jumped in lake and swam to town, it continued on and started divebombing the citizens and soldiers in town. Bodies everywhere. 10 minutes in, with soldiers hitting it and witch hunters shooting arrows, and it was at 70% hp and I got too eager and it jumped and hit me. Was fun though to see a mob cause utter chaos. Obviously not intended, because the npc shouts and dialog were more in tune with what they would yell towards me if I went berserk there instead of a giant bird. No idea how the game would turn out though if I had managed to kill it like that. 80% of the marketplace in Novigrad was wiped out. Tempted to see if I can pull it towards the soldier camp at the bottom of the map.