After I fixed the NPC = Hit.Parent, that was the error that was shown.
It’s specifically indicating this line of code:
NPC.Head:FindFirstChild("BillboardGui"..Int).Enabled = true
Currently, I do not have the BillboardGui enabled (since I don’t want it to always be above their head)—perhaps that’s causing an issue?
Before fixing, the error was regarding the Num value but that isn’t showing up in the output anymore so that’s fixed.