For the sake of balancing and to add better variety, I'll probably go with Dullahan after all. 

For his execution, I figured a few things to balance it. One is to lower the check to a standard LCK check, instead of a high one. The target cannot be interfered with, whether it's an ally or enemy, which makes allied servents pinning the target down impossible. While this applies to the target, this doesn't apply to Rider himself, and allies of the target can just throw Rider off from using this Phantasm. Lastly, if the target were to survive the attack with the LCK check or something similar, they are immune to it until the next night. This is mostly to balance the execution to not being spammed, while also keeping the theme appropriately

I honestly still believe Dullahan's other weaknesses counteract his strong Noble Phantasm to some degree. And I'm sure it goes without saying that he'd be instantly identifiable the moment he starts using his head, which is almost neccessary for him to act, anyway. Despite there being multiple versions of the legend, the fear of gold is almost universal.

As far as interactions go, I've had a few silent characters that were met with success. I actually enjoy the aspect of having a character unable to truly speak, as it gives myself as a writer more of a challenge to develop my character welll.