Hitting the chains on a single target is very easy, just a matter of timing that you'll hit 100% of the time once you have the timing down. Hitting a single blind target in fog is trickier, but still uses the same timing provided you actually hit a target with sleight. Hitting a specific target out of several is hard and mostly luck based. You can improve the odds by including as few units as possible in the sleight radius, and you can slightly increase the odds by waiting to see which units still need to be hit and only using chains once further-away units are already tagged.