Gazul is much like Avalon in the sense that he is a support hero. Where Avalon supports living armies Gazul buffs the undead. Besides his support auras Gazul has a very powerful ability which is Sacrifice, which summons a giant bone golem. This golem is very powerful if used properly and is critical in your defense against lich players who mass spiders.

Resurrect (costs 1 mana)
Gazul resurrects corpses in the target area into skeleton warriors. The stronger the target unit, the less likely it will be resurrected successfully. Any remaining resurrected troops will join your army at the end of the battle. The number of units resurrected cannot exceed 10.
This ability can be used as an emergency troop maker, during battle it can summon just enough troops to win you the day, but be requires Gazul to have very high magic otherwise it may fail to raise any undead. Any undead that survive the battle will be added to your army so you can use this ability to build a lich army for basically free if you spend enough time in quest battles.

Fearsome Aura
Gazul’s presence always strikes fear in the hearts of those around him, increasing morale decline for all troops on the battlefield by X%
Do not get this skill unless you are playing lich, as it will also affect your own troops which will make them flee battle more easily.

Skeleton Sacrifice
Gazul sacrifices skeleton troops in the specified area, and summons a massive Skeleton Titan with X bas HP and X base damage to assist in battle. The greater the amount and strength of troops that are sacrificed, the stronger the Skeleton Titan will be.
Max this skill. It summons a giant titan which targets giant units first, use this skill on a pack of skeletons you have been getting from Resurrect and make this thing a monster and it will kill those pesky spiders for you no problem.

Skeleton Mastery
Gazul excels at leading skeletal troops into battle. When he takes to the battlefield, all allied Marauders, Ravagers, Stalkers, Acolytes, Occultists, Warlocks, and Pikemen have their damage and max health increased by X%.
As it currently stands undead units are not viable and thus this skill isn’t worth your time.

Immortal Strength
Gazul’s immortal power grants extra power to undead units around him. When he is on the battlefield, all allied undead units have their max hit points increased by X%.
Same as above comment.

Soulless Scourge (costs 5 mana)
Costs 5 mana. Gazul summons a swarm of undead spirits that sweep the battlefield, dealing X damage where they pass.
This skill is a powerful spell that will kill a vast majority of the enemy army, using this to completely crush a section of the battlefield.

Building Gazul
One point into Resurrect so you can raise corpses and have some skeletons to sacrifice for Gazul’s Skeleton Sacrifice ability. Max Skeleton Sacrifice, Max soulless scourge. If you play all mech units or as lich max Fear Aura.

Equipping Gazul
Same as Vega, max his magic stat and get the +1 to skeleton sacrifice item, that’s all. Refer to Avril item setup for an idea of what items to equip.