I keep forgetting about killer weapons in this game for some reason. I think I gave Ferdie one for a short time in my CF run to help him catch up when he fell a bit behind my other units, and Byleth with a killing edge was invaluable as part of my strategy against CS's final boss, but the rest of the time I barely remember that those weapons even exist! Still, I should consider slapping one or two on to Ignatz on my Deer run, and considering Ingrid gets a decent number of crits even with more regular weapons, I don't doubt she gets solid mileage out of them.

Yeah, that's the one. I was able to take him out with Ashe (bow knights are another lifesaver thanks to their humongous attack range) but the poor boy only just managed to survive the following attack from the guy on the ballista thanks to Sylvain throwing a Physic spell at him. It's risky, but it's worth doing because it makes all the other Those Who Slither enemies leave.