A custom NPC whose festival locations have been established using TMXL are only shown on the host machine during multiplayer play, not on other participating players' machines that are running with the same mods. The host can see and interact with the custom NPC; the other players can neither see nor interact with the NPC during the festival.

I wasn't trying anything overly fancy, just the straightforward stuff:

{
"name": "Candy Festival Locations",
"version": "1.0.0",
"author": "CMAlbrecht",
"festivalSpots": [
{
"name": "Candy",
"map": "Town-EggFestival",
"position": [26, 73],
"direction": 0
},
{
"name": "Candy",
"map": "Forest-FlowerFestival",
"position": [5, 32],
"direction": 1
},
{
"name": "Candy",
"map": "Beach-Luau",
"position": [21, 7],
"direction": 2
},
{
"name": "Candy",
"map": "Beach-Jellies",
"position": [40, 36],
"direction": 2
},
{
"name": "Candy",
"map": "Town-Fair",
"position": [49, 59],
"direction": 2
},
{
"name": "Candy",
"map": "Town-Halloween",
"position": [41, 15],
"direction": 3
},
{
"name": "Candy",
"map": "Forest-IceFestival",
"position": [66, 16],
"direction": 1
},
{
"name": "Candy",
"map": "Town-Christmas",
"position": [32, 56],
"direction": 2
},
],
}