Will there be a climatic battle between fighter and BM???
 

Well it seems so...

No.

Reasons:
1. Nothing is seriously climatic. This a comedy comic.
2. Fighter and Bm are the most bestest friends ever.
3. There are too many question marks in your title. Not a real reason, just wondering why this question seems to be this important to you.

Realy though, anything could happen, I just don't see this.

B-b-b-but what about the ominous foreshadowing comic? What about it?

Ever since Nuklear Age, I tend to expect all of Brian's works to begin a descent into GET FUCKED at some point.

My money's on an anticlimactic battle. It'll come down to just the two of them in the end, I agree, but all the drama will be in their words -- the actual fight will be almost an afterthought. Their power is of such different kinds that they couldn't really have a prolonged battle. My guess is that BM will be about to ascend to some ultimate power and destroy the world, and Fighter will kill him at the last moment.

I do beleve that this has been brought up before.

I wonder if the OP expected Brian to swoop in and tell us all exactly how it ends, just because he asked :p

As for 434, the only thing that doesn't seem to be examined / explained is 'red boxes' use of "WE thought it'd be funny". That just doesn't make sense to me.

"We" as in "the whole group." That always struck me as the easiest thing to explain. :p That episode is seriously weird and could be anything from an account of the final events in 8BT written in code to a red herring.

As for the climactic battle, I don't see it at this point, but it's certainly possible. ... not much else I can say about it, really.

My take on 434 is it's BM dying and talking to either Fighter or WM, after either

1. Saving WM from Chaos and/or Sarda semi heroically
2. Killing Chaos and/or Sarda
3. Attempting to betray the LWs to Chaos(can't see this happening if Sarda is Chaos) and getting backstabbed by Chaos
4. For a reason that's could be one of the above, he's accidentally mortally wounded by Fighter.

Or what I consider the most likely
5. Amazingly getting mortally wounded by Garland(who is not Chaos but is there none the less) in a moment of either actual competency at evil after Chaos/Sarda is beaten.

So no I don't think there will be a climactic battle between BM and Fighter. The closest is Fighter accidentally killing him.

Note the second-lowest panel. Somebody's probably already mentioned this, and probably in a prior thread, but doesn't that look like the hem of White Mage's robe? Spattered in blood? Is it just me? Could be marinara, I suppose, especially given WM's professed love of Italian food.

I suspect that it's WM addressing an entity who is either
a) Sarda / Chaos
b) Black Mage merged with Chaos

And I submit that any and all who disagree are quite possibly better at this than me.

I always thought that it was the "creator" WM talking to BM the demon king
but does sound more likely

maybe after BM fused with chaos he accidentally killed WM thus unleashing the Creator WM (you know like the Phoenix in the X-MEN)