This looks really cool - However, "half damage" on fumbling an attack is kinda confusing to me.
I know that the fumble is before modifiers, but given that the fumble only happens when you roll a 1, won't that usually mean that the damage dealt is 0 most of the time, given that "half damage" happens when the opposing die (before modifiers) is a 2?
Even with a +2 in Strength for the attacker, that would result in damage of 3-2=1, wouldn't it? Hope this makes sense! Other than that nitpick, it looks great. Have you tried it at the table yet?