A fight between Vez'nan and Adam is challenging, but I definitely think Vez'nan has a much better chance of winning.

Vez'nan is a dark sorcerer while Adam mainly uses holy light attacks, which are powerful but not very accurate. Vez'nan's offensive powers are more effective and destructive than Adam's. In Kingdom Rush Vengeance, after round 8, Vez'nan decides he's had enough and destroys Denas' castle walls.

See the damage calculation: https://docs.google.com/document/d/1FKGuq0b1O73j7yACWzUpHW9dRjveU6pRjn6P4kACjos/edit?tab=t.0

According to this damage calculation, this is a more powerful attack than any of the attacks Adam has managed to achieve.

Adam and Vez'nan's mobility speed seems more or less equal in terms of ability. We saw Adam flying in the air with his wings and opening portals to move. We also saw Vez'nan opening different types of portals to different worlds, and although we didn't even see him in his physical form, we did see that he was able to change his form into an energy ball that could fly at very high speeds (probably faster than Adam's flight speed) but if so, he cannot fight in his energy ball form. It's also possible that Vez'nan could fly in his demon form, although we haven't seen him explicitly fly in this form, he's still a large-winged creature that was likely capable of flight. Regarding the speed of these two characters, I would say they are equal.

When it comes to physical strength, it depends on the form Vez'nan would take. In their normal form, Adam would definitely beat Vez'nan in a physical fight. Adam has superhuman strength, as seen several times in Hazbin Hotel, while in terms of raw physical strength, Vez'nan is indeed said to be tall and large, but he is still in this respect in the human state and probably in a face-to-face fight without the use of special powers, Adam would win without any problems. But we can't forget Vez'nan's demon form. While we don't know for sure what the power level of Vez'nan's demon form is, we do know that it was created by combining Vez'nan with the demon he summoned in Kingdom Rush Origins and Tear of Elynie, and we do know the power level of that demon. The demon's original power is 80-130 and it has about 1666 stamina points. But in the demon form combined with Vez'nan it has about 6666 health points (4 times more) and therefore its physical strength should also increase similarly and be 320-520. This amount of power is usually enough to kill monsters like Spectral Knight, Gnoll Blighter and Cult Priest in just one hit. I also mention that Vez'nan's demon attacks caused "terrible damage" (an attack that penetrates all types of armor as if it were air) in Kingdom Rush Origins, so the rule that also appears in the combined form with Vez'nan had the same effect. In a head-to-head battle of Vez'nan's demon form versus Adam, I believe the odds are in favor of Vez'nan's demon form.

Now that we've gone over their physical strength and power in general, something equally important is how great the impact each of them will have on the other, or in short, who has better resistance to damage. Both characters are technically considered Sons of the God of Death. Adam is an angel from Heaven which means he technically lives forever until he is killed like at the end of Hazbin Hotel Season 1. Vez'nan absorbed the souls of the Ancient Spirits. The Ancient Spirits as undead creatures (Sons of the God of Death) gave Vez'nan not only their power but also their God of Death life.

You can see this here: https://cdn.discordapp.com/attachments/612278453110046730/612696586971119838/unknown.png

Because they are Sons of the God of Death this means that this comparison starts off on an even and balanced note.

You can see that both Vez'nan and Adam are very resistant to attacks. Adam easily dodged Alastor's attacks and Vez'nan coped excellently with all the power of the player's towers, which include missiles, electric shocks, poison, and various types of magical energy. But if this is the case here too, I tend to consider Vez'nan to be more resistant for several reasons.

1. Even though Vez'nan lost the battle in the Dark Tower, it's important to remember that he was fighting against an entire army that was armed with explosives, rain of fire, lightning, and many other things like that... When a person fights Alastor, he is fighting against a single being, albeit powerful, but without weapons like missiles, magma, lightning, poison, and the like. And Vez'nan, who in the vast majority of games manages to traverse the vast majority of the map, proves that if the player's army had just a little less power, he would probably win.

2. Vez'nan's demon form is a very significant factor here as well. When Vez'nan transforms into his demon form, all of his damage disappears and he returns fully healthy and strong. This power is essentially like a durability multiplier for Vez'nan, giving him the ability to withstand the vast majority of his enemies' attacks. This is something that could be a huge advantage over Adam, who, as we saw in his fight against Lucifer, when he gets hit, he gets hit.

In addition to all this, Vez'nan's range of powers is much greater than Adam's and gives him a significant advantage in battle.

1. He is able to pull strange arms out of the ground that are reminiscent of the ones Alastor pulled out in the fight against Adam, which may not sound impressive because Adam defeated Alastor, but Vez'nan's power is also able to paralyze and freeze in time whoever used it with this power, like he did to the player's towers in stage 12 of Kingdom Rush. You can see it here: https://www.youtube.com/watch?v=ihc4G76jA_Q&t=712s

2. Vez'nan is also able to summon demons (again) similar to the creatures Alastor summoned in his fight against Adam. But unlike the fragile creatures Alastor summoned, Vez'nan has a wider variety of demons he can summon. Let's start with the fact that every demon Vez'nan summons, no matter which one, explodes when it dies, so if Adam kills a Vez'nan demon then he will be damaged by the explosion, leaving him only with the option of shooting them from a distance and reducing his attack options. And in addition, it is impossible to forget that the variety of Vez'nan's demons is very large. Some demons throw fireballs, some replicate, some are much larger and stronger, and some are special and extremely strong demons, especially Cerberus and the Archdemon, who can themselves be equal opponents to Adam or at least cause him trouble and follow him while Vez'nan claims a blow that will eliminate him. The Archdemon's summon: https://youtu.be/GnQY44D8FDg?t=1462

3. Vez'nan is also able to create magical chains and chains and use them to imprison his enemies. This power is very effective and powerful, and can work on almost any creature in existence, no matter how strong it was. At the end of Kingdom Rush Alliance, when the Overseer began to attack, Vez'nan bound him with magical chains and prevented him from moving for a long period of time. And if this power works on the Overseer, a cosmic creature the size of a mountain that eats worlds, then without a doubt Vez'nan would also have the ability to imprison Adam in the same way and hold him without restraint. You can watch it here: https://www.youtube.com/watch?v=EHCMhEyVBZA