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Not sure how this would work out. I'm pretty sure you can give an eternal kindred a mundane great weapon and as the book says you only lose eternal guard fighting style if you take a magic item or magic armour, you still get the 5+ AS. BUT do you get the strength bonus and an additional attack, as the fighting style says 'they are considered to fight as if they were armed with two hand weapons' in B2B, or can you choose between the theoretical 2 hand weps. or the great weapon? (unless I'm missing something )
Thanks in advance
I'm pretty sure the eternal guard fighting style rules supercede any other weapon rules, so taking a great weapon would effectively do nothing. You can't choose to turn off (most) special rules. That said, if there is a FAQ errata about this I'm unaware of it and thus could be wrong.
Swarm is correct. Giving him a great weapon will have no affect. He would still fight as if armed with two hand weapons without the great weapon bonus.
I am right 94% of the time, why worry about the other 3%.