Sounds to me like you just didn't prepare well enough ahead of time.. I will bring a bench, stone and my hoe with me.. level out a HUGE area around the boss so there is no water and good ground for me to scramble.. I'll have my portal on top of a nearby crypt or abandoned building.. It sounds like you actually fought him partially at night time.. seeing how you had a wraith... that's not good. Was there no way once he was summoned to back up away from the plains locations?