Nearly there, here is my teaser..

[Irish Daigle]

First, your Belial card has a typo in Posessor, should be Possessor.

Second, am I reading it right that he has 2d6 fight dice, as in he can have potentially 12 fight dice? I think maybe I'm just confusing my D&D with my LNoE.

And really, I would guess tactically the advantage to picking up a Relic is to run the hell away from the church with it. Since they need all 4 Relics for the Ritual, even getting one of them away from a Relic Zombie and then just play "chase the meat" can win the game. I expect Heroes wouldn't risk it unless it's already close to the end of the game and Belial is one or two turns from coming into play. Because realistically, if you manage to ward the Relic Zombies off long enough, but in the last two turns before sunrise Belial comes out, the Zombie side has as good as won. It's a suicide tactic, more or less, one that can definitely pay off if circumstances are right.

And I would think anyone who plays this more than once or twice would quickly discover the best way to win against Belial is through Ranged weapons that don't insta-kill. The reality of rolling a 1 against Belial, which makes the Hero instantly lose a fight, will be all too common, especially if they're rolling in with three or four fight dice. Going melee toe-to-toe with Belial would then be tactically unsound unless you were Johnny with an extra wound to take and no extra fight dice. Even then going melee against Belial is unwise because he almost definitely has four Relic Zombies hovering around him.

To me it sounds like it very unfairly gives advantage to the zombie side. It would be like playing Pandemic in that the zombies will usually win.

If I were playing a Hero in this scenario I'd probably tactic it out like this:
1. Ignore three Relic Zombies and spend your time griefing the one furthest away from the church.
2. The other three players concentrate on managing the regular zombies and stocking up items, rotating out the Relic Zombie griefer by turn five or six so that Hero can go stock up on a couple of useful items as well.
3. By turn seven or eight I imagine the other Relic Zombies have delivered their relics, and the currently-griefed Relic Zombie is still somewhere around halfway to the church.
4. If the Relic Zombie just keeps making progress slowly but surely and it looks like he will inevitably make it to the church anyway, I would make sure I have four to five turns with Belial out and about to try and deal with him, which means potentially just backing off and letting the Relic Zombie go. Stock up quickly on battle gear if you can, then zombie barbeque the Relic Zombies the moment they appear again outside the church, and everybody dogpiles Belial in an attempt to finish him off.
5. If there are just two or three turns to go, and suddenly things go bad and it looks like Belial is going to get summoned, I would do my best to kill the Relic Zombie, then decide whether it's worth the risk to try and pick up the Relic and flee with it.

Belial getting summoned makes winning the game extremely difficult, especially if it's going to happen in the last three turns of the game. I would probably change the D6 for Relic-cursing into a Relic Zombie Hero from "instant Zombie on fail" to "wound on roll of 4 or less". It definitely needs to retain its extreme risk element, but it's like a 90% chance of failure by turn 2 of holding a Relic the way it is now. Those are extremely long odds, and it would have to be the most dire of situations before I would realistically attempt it. Like "we're losing the game next Turn no matter what, so what have we got to lose" scenario. A common gameplay element shouldn't be quite that risky. Still very risky with wounds 66% of the time.

Edit: I forgot to mention that I definitely like the addition of a "boss" monster to scenarios. It definitely adds some interesting flair to a scenario that could otherwise end at "big bad gets summoned, we all lose" if we have a chance to try and kill him.