I've always liked
CustomNPC's for that purpose. It offers highly customizable npcs and allows you to create custom mobs and quests. You can use skins found online (or extract them from my packs) for your entities.
Using this mod, you can create dialogs, have players kill a certain enemy, have players collect an item for the questgiver and even ask players to move to coordinates in your world. You can choose to have static NPCS or have them move in a certain area.
The mod is compatible with other mods; if you have a mod that adds mobs (such as Twilight forest), you can use those models too. I've used it to create a decent Walking Dead experience for me and my friends in the past.
