I would not give an NPC a spell like that so I suggest this:
Power Word Incapacitating Tickles
You utter a word of power that can compel one creature you can hear within range to fall over squirming and laughing, begging you to stop the imaginary tickles until you choose to end it’s effect. If the target has less than 100 hit points it takes effect, otherwise the target enjoys the sensation that feels like tummy rubs and is charmed for one round.
I would not give an NPC a spell like that so I suggest this:
Power Word Incapacitating Tickles
You utter a word of power that can compel one creature you can hear within range to fall over squirming and laughing, begging you to stop the imaginary tickles until you choose to end it’s effect. If the target has less than 100 hit points it takes effect, otherwise the target enjoys the sensation that feels like tummy rubs and is charmed for one round.