Belial is the first true multi-staged boss in Diablo III, and several elements of his fight seem to act as call-outs to other major boss battles in other games- particularly other, older RPGs that fit in the ‘action-RPG’ subgenre.
The initial part of the fight is fairly straightforwards- there is no dealing directly with Belial at first. All you have are a large number of the serpentmen you’ve been fighting for large parts of Act II. Really nothing special here- a bit of patience and some area attacks will smear them all over the expensive marble floor as easy as cutting a stick of warm butter.
The second part of the fight is where things start to get interesting. Coming down of his high horse (throne?), Belial starts to face you himself.
Second-stage Belial features three main attacks. The first is a charging attack, a straight line that Belial travels towards his target with a protracted poisonous punch. This is easily hampered or even neutered by slowing effects. The second is a spread of three wads of poisonous energy that he launches along the ground at you- easily avoided at range, but if you’re a melee character just suck it up and find a way to endure. Finally, he will occasionally summon more serpent-men. If you’re not worried about getting hit by him, though, you can generally knock him out of second phase fast enough to keep him from ever doing so.
The second stage of Belial is a bit challenging, mostly in the event you’re not a melee type and have neither a melee type nor a templar with the aggro-drawing powers along with you. This can generally be alleviated by a good bit of poison resistance and/or a high Health rating.
The final stage of Belial is the true challenge. In the third stage, he replaces the throne area with a giant himself, leaving you (and any of your allies) alone on the semicircular platform. Once he’s done this, the only way to hit him in melee is by running up to the inner edge near the middle of the crescent and attacking him- ranged characters generally just have it a lot easier here.
Third-stage Belial is conceptually easy, but actually rather tough. While most of his attacks are preceded by large green glows that make it easy to see where he’s going to hit and get out of the way, in practice this leaves you with very little time to actually wail on him and topple his massive healthbar.
There are two ‘ranged’ attacks that third-stage Belial uses, and three variations of a melee attack as well. The ‘ranged’ attacks are fairly simple- the first is a belched-out cone of poison that he sweeps across a large part of the floor-arc. This one doesn’t come with much warning, but if you stay front and center, you’ll always start off a decent distance from the gaseous cloud and stand a fair chance of evading it if that’s your interest. The second ‘ranged’ attack is a hail of green, poisonous ‘meteors’. While he is using this attack, Belial keeps his arms planted in the platform, and each ‘meteor’ is preceded by a green glow that starts about a second before the impact. There are a lot of them, though, and they’re only semi-random- so standing in one place is a good way to go squish.
His ‘melee’ attack comes in two forms- the first form is a single downward punch that stabs his pointed arm into the floor. As with the meteors, this is preceded briefly by a circular green glow- and while that makes it easy to avoid, it makes his other fist attack harder to evade. The other attack is similarly foreshadowed by the green glow- but rather than punching down, he slams an arm down across the arc of floor at that point. This makes dodging the green glow towards or away from Belial himself far less effective, and it covers a larger area ‘horizontally’ as well, so don’t get too used to dodging the downward stab. Just to make things worse, he may follow this up with a second strike with the same arm- and roughly half of the time this is followed further by slamming that arm down a third time, and while all three strikes are predicted by the glow, the third one uses his other arm as well, and that arm does not leave an ‘impending shadow’ in noxious green.
This makes Belial a boss who is all about prediction- and that prediction is made difficult. The need to keep moving out of his attacks makes the fight very difficult- you’re left with the choice of dodging like mad and taking quite a long time to break through his defenses, or just accepting a certain amount of punishment in return for being able to actually end the fight.
