A character needs to remain completely calm in order to trigger Galael's weakness, kind of serenity, or in the other hand, emotions like happiness or hope (it does not specify these two but few Lord of Nightmare are weakened by those emotions).
I wouldn't count on Zagor activating that weakness. It may happen, on occasion he's shown to indeed embody positive emotions and become a sort of paragon to them to the point he is chosen to match against some of the greatest evils in existance, but those are far in-between and there's generally a big charge of emotional investment within. I don't think Galael has the needed emotional connection to Zagor to him feel anything greater than the usual, fight-related stuff, which is adrenaline, a certain dose of anger, a motivation to do the right thing, nothing that really would help much in that sense.
That being said, here's my analysis: (Sidenote: Jesus, I need to clean up my english mistakes... I always do the dumbest mistakes-)
Physically, Galael seems stronger, even if just a bit, and they are close enough in tier that properties like material hardness are very important. His body, if he becomes a spider-like creature with a chitinous shell, would make him a harder target, which is a bad thing against most of Zagor's weaponry. Knives and bullets wouldn't do much, I don't think, and Zagor would need to land very clean hits with his hatchet and blows if he wishes to do some damage. To be fair, though, Zagor does not have any difficulty in landing very precise strikes with either his hands or his hatchet, and he hits significantly harder with his hatchet than without, even compared to what would be normal to someone using a weapon. An interesting bit about Zagor is that he can be significantly boosted through strong emotions, to the point of easily beating/matching people otherwise close or stronger than he is. It wouldn't matter much here, I don't think, as it usually requires emotional motivation and connection to what is happening, but it possibly could influence this.
One thing of note is that Galael has a superior LS, which could be troublesome in a grappling situation. While Zagor has some feats such as overpowering wild animals that can get him to match Galael's more casual LS, he certainly can't grapple with the 1-ton-lifting stuff he does. Zagor does appear to have a superior skill in martial arts and grappling, though, which could be very useful - he has experience in using the momentum of enemies and technique to throw, take down or even chokehold them despite them being very superior to him. Case in point,
Bela Rakosi, which is so much stronger than Zagor that he can easily overpower him with one hand and ragdoll him around, but once Zagor was ready for him,
he easily threw him off a cliff by using technique, and there are other examples of Zagor overpowering people a bit stronger than he is using skill. Would that allow him to overpower Galael?... I don't think so, but considering that Zagor is smaller than Galael and has a lower center of gravity, I also do not think that Galael can easily use the superior LS to grapple him.
On their powers, this is the part that makes me wonder, because I can see both of them working what they have to their favour. Tackling Galael's own first (Which you guys please do correct me if I make any wrong assumptions. I'm basing only what I can see on the profile and what has been said here), I'll say the fear-based stuff wouldn't be very useful (Which is good, Zagor is on an already precarious strength position here) as Zagor not only has supernatural willpower, but he is very much used to very scary, otherworldly stuff. I don't know how the Ice Manipulation or Body Control work like, so I'll refrain commenting. Surface Scaling is very interesting (And I should add that to Zagor's profile too, although Galael's probably better at it than Zagor is) and can influence the fight depending on how Zagor goes about it. His durability negation is, however, a very powerful tool here. I don't think Zagor would try to block any strikes as the hatchet really isn't optimized for that, and he isn't someone to try to take hits as he is more of an acrobatic fighter, but if Zagor gets hit cleanly, he's gone.
Zagor has basically superior skill in many different fields, which he'll need to apply because a slugfest isn't optimal for this scenario. It isn't really impossible for him to win a direct fight, not even extremely hard, but he'll be losing way more than he'd be winning, as he'd need to incapacitate Galael quickly. He has good pain tolerance, and has the stamina to fight at full power for a good amount of time, and the skill to hit more than he'd get hit by Galael, and Galael has been said here to not really try to block and parry attacks, which would be bad for him. But Galael is tireless, has considerably superior reach (Which is a
big thing in melee) and not only he is stronger, but his strikes can go right through Zagor, so I'd bet on Galael on that scenario. But Zagor is wily too, and he isn't hesitant to retreat after an initial scuffle, and he would use the environment to ambush Galael and do surprise attacks, maybe even using the vines on Galael's greater frame.
In fact, it wouldn't be OOC for Zagor to retreat quite a bit deeply into the forest, fashion some traps and improvised bow and arrows (possibly with poisoned tips, which, to be fair, wouldn't change much), and use everything there to whittle him down or even to entrap the potentially longer limbs and larger size.
But it is only a possibility, and I don't know how Galael would react to such scenarios, but it is a fun thought and something very possible indeed.
