>>82877051He sucks to fight the first time, learn his attack pattern (watch someone else do it in a guide, text doesn't help) and use the best healing food you can get (I'm a main, I used sea turtles for a 21 heal and combo ate with karambwans; consider curry, it heals 19, is easy to get and still lets you combo-eat with karambwans).
The flail is extremely inaccurate, so do everything you can to maximize your attack accuracy and magic defense instead of your max hit.
You should be wearing a Helm of Neitiznot with a glory, karil's or black/god dhide body/legs, barrows gloves, dragon or rune boots, either an Ardy cloak (prayer bonus) or a Fire Cape, Explorer's Ring (prayer bonus) or a Berserker Ring and whatever blessing you can (ammo slot item, Rada's Blessing comes from Kourend diaries and the medium-tier one is equal in strength to the ones you get from clue scrolls).
Hope this helps.