Last session, a player character cast Hypnotic Pattern on a Roper which had another PC restrained in one of its tendrils. The Roper was incapacitated. A blue dragon wyrmling then used its lightning breath on the restrained PC, hitting both the PC and the tendril, destroying the tendril. I had ruled that the player was no longer restrained and the Roper was no longer incapacitated. However it says that the Roper takes no damage if a tendril is destroyed, and that Hypnotic Pattern only ends if a creature takes damage.

When I thought about it further, namely what would have happened if a monk used Stunning Strike on the tendril, I would have leaned toward ruling the other way, that the Roper was not stunned, just the tendril, as it is a different target than the creature, technically.

Opinions?

 Thinking from a RAI - that line on no damage to the Roper I think is merely meant to say no damage is done to the HP total, but I think in this situation I would say the Roper should be able to break the hypnotic pattern.  While you can target the tendrils individually, they are not separate creatures.  So damaging the tendril is still damaging the Roper, imo, for riding charm effects.  Similarly since the tendrils are not separate creatures the Stunning strike would still stun the entire Roper not just one tendril.

I'm sure someone will come in yelling about the "correct" RAW and RAI but that is how a read the words written.  No damage to the Roper's main health pool, but you still dealt damage to the creature.

That seems like a reasonable ruling to me.

I agree. I would probably rule that breaking the tendril has the same effect as doing hp damage to the roper. It's going to feel the tendril breaking and that will "wake it up" or "break the charm" or what have you.

Thanks for the input everyone! However, I was thinking if a monk hits the tendril, destroying it, and then attempts stunning strike, does the stunning strike still work on the Roper?