Abazigal is a lawful evil chromatic blue dragon Bhaalspawn and he is also a member of the The Five, whose goal it is to destroy their kin. He has the ability to take the form of a blue skinned human. Abazigal has a son, Draconis, who is also a Bhaalspawn himself, but he is a green scaled dragon. Abazigal is leading an army of half-wyverns and dragons. He can be found in his lair. He is always immune to the effects of Hold Person, Web, stun, Poison, slay, Sleep, charm, Slow, Grease, entangle, silence, berserk and panic, and he is completely immune to electrical damage and has 65% magical resistance. In his dragon form he is also immune to Time Stop, in the Enhanced Edition in his human appearance as well.
Make sure you kill as many as possible Ice Salamanders before confronting Abazigal, who will start a short conversation before fighting and make sure all party member are under effect of Remove Fear. He will start the battle and then he will use the ability Hardiness, which gives him 40% resistance to any physical attack. Let one party member tank him and try to take 290 hit points without using powerful spells&abilities which are needed when he takes his dragon form. He may also use the abilities Kai and Whirlwind Attack and the 3 Potions of Superior Healing which he can use.
Now he has taken his dragon form and while doing so, he will kill any summoned creature around him at the time and use abilities as Dragon Fear, Wing Buffet and will do physical attacks with his claws, which also inflict electrical damage. Now he has a basic resistance to all physical damage and the effect of Hardiness should not be active by now. If there are not enough ice salamanders dead, you probably will get in trouble now for not doing so.